Electronic scanning type radar device, estimation method of direction of reception wave, and program estimating direction of reception wave

ABSTRACT

An electronic scanning type radar device mounted on a moving body includes: a transmission unit transmitting a transmission wave; a reception unit comprising a plurality of antennas receiving a reflection wave of the transmission wave from a target; a beat signal generation unit generating a beat signal from the transmission wave and the reflection wave; a frequency resolution processing unit frequency computing a complex number data; a target detection unit detecting an existence of the target; a correlation matrix computation unit computing a correlation matrix from each of a complex number data of a detected beat frequency; a target consolidation processing unit linking the target in a present detection cycle and a past detection cycle; a correlation matrix filtering unit generating an averaged correlation matrix by weighted averaging a correlation matrix of a target in the present detection cycle and a correlation matrix of a related target in the past detection cycle; and a direction detection unit computing an arrival direction of the reflection wave based on the averaged correlation matrix.

CROSS-REFERENCED TO RELATED APPLICATION

This application is a National Stage entry of International ApplicationPCT/JP2008/073606, filed Dec. 25, 2008, which claims priority toJapanese Patent Application No. 2007-331567, filed Dec. 25, 2007,Japanese Patent Application No. 2008-002312, filed Jan. 9, 2008, andJapanese Patent Application No. 2008-002313, filed Jan. 9, 2008, thedisclosure of the prior applications being incorporated in theirentirety by reference.

TECHNICAL FIELD

The present invention relates to an electronic scanning type radardevice, suitable for mounting on a vehicle, which uses a reflection wavefrom a target corresponding to an emitted transmission wave in order todetect the target. The present invention also relates to an estimationmethod of a direction of a reception wave, and a program estimating adirection of an incoming wave to be used for the above estimationmethod.

The present application is based on Japanese Patent Application No.2007-331567, filed on Dec. 25, 2007; Japanese Patent Application No.2008-002312, filed on Jan. 9, 2008; and Japanese Patent Application No.2008-002313, filed on Jan. 9, 2008.

BACKGROUND ART

Conventionally, an electronic scanning type radar has been used as aradar mounted on a vehicle, which utilizes the system of an FMCW(Frequency Modulated Continuous Wave) radar, a multifrequency CW(Continuous Wave) radar, a pulse radar, and the like.

According to each of the radars mentioned above, an estimation method ofa direction of an incoming wave of an array antenna is used as atechnology for detecting a direction of an incoming wave (or a receptionwave) from a target.

An example of this estimation method of a direction of an incoming waveis a null operation method (refer to Non-Patent Document 1 and 2, forinstance) known as a super-resolution (high precision) algorithm such asa beam scanning method like the Beamformer Method and the Capon Method,a linear prediction method like the Maximum Entropy Method (MEM: MaximumEntropy Method), the Minimum Norm Method, MUSIC (Multiple SignalClassification) Method, and the ESPRIT (Estimation of Signal Parametersvia Rotational Invariance Techniques) Method.

Further, the estimation of the direction of the incoming wave, used by aradar mounted on a vehicle, is conducted by a method (refer to, forexample, Patent Document 1) using solely the digital beam forming (DBF:Digital Beam Forming) of the Beamformer Method, or by a method (referto, for example, Patent Documents 2 and 3) combining the DBF and theMaximum Entropy Method in recent years in order to enhance the detectionaccuracy of the arrival direction of the reception wave (or theresolution performance of the target).

Moreover, in order to apply a super-resolution algorithm such as MUSICto a vehicle-mounted radar, a microprocessor is used which is utilizedfor vehicle-mounted radar with a low arithmetic processing capacity,compared to normal personal computers. Therefore, a method is developedby simplifying an estimation algorithm (refer to, for example, PatentDocuments 4, 5, 6, and 7).

According to the super-resolution algorithm such as MUSIC, mentionedabove, a correlation matrix is generated from data of reception wavesreceived by each array antenna. An eigen value calculation is conductedby this correlation matrix. Thus, the arrival direction of the receptionwave is detected. Here, the eigen value calculation (computation) refersto a calculation obtaining the eigen value and the eigenvector.

At this time, the super-resolution algorithm generates a correlationmatrix by an ensemble average of the reception data because the accuracyof detecting the arrival direction enhances as the noise element of thecorrelation matrix is removed.

For example, the FMCW radar uses a correlation matrix generated byobtaining highest possible number of samples of a data set of thereceived beat signal (a temporal sequence data of a certain period oftime, which can be converted to a data in a frequency domain) andobtaining an average. The number of samples is called a snapshot number(refer to, for example, Non-Patent Documents 1 and 2).

However, according to the vehicle-mounted radar, the distance from thetarget and the relative velocity change constantly. Therefore, even ifthe snapshot number is increased nebulously, the accuracy of detectingthe arrival direction of the reception wave does not necessarilyincrease.

On the contrary, in order to increase the snapshot number within acontrol cycle (or a detection cycle such as 100 ms) for detecting thetarget, the frequency resolution operation corresponding to thereception signal must be conducted simultaneously for a number of timesmultiplying the number of array antennas and the snapshot number. Thus,there is a limit on the number.

Patent Document 4 describes a method in order to enhance the accuracy ofdetecting the target without increasing the snapshot number. Accordingto this method described in Patent Document 4, for example, acorrelation matrix is stored for each beat frequency at the previouscontrol cycle (or the control cycle immediately prior to the previouscontrol cycle). Further, this method obtains a weighted sum (weightedaverage) of a correlation matrix of a beat frequency, for which a targetexists in the present control cycle, and a correlation matrix in theprevious control cycle (or the control cycle immediately prior to theprevious control cycle) having the same beat frequency. Moreover, PatentDocument 4 describes a method which stores the weighted averagedcorrelation matrix for each beat frequency, and obtains a furtherweighted sum of the correlation matrix of a beat frequency for which atarget exists in the present control cycle and a correlation matrix withthe same frequency obtained as described above by weighted summation.

In addition, Patent Document 5, mentioned above, discloses a method forincreasing the snapshot number by averaging each correlation matrixgenerated for a frequency indicating a peak value, from among the samepeak waveform for which a target exists at a beat frequency, and for afrequency in the vicinity (for example, ± two frequency resolutions).

According to this Patent Document 5, an average of the correlationmatrix in the frequency domain is further averaged by using a pastcorrelation matrix.

Next, Patent Document 6 describes estimating an arrival direction of thereception wave by combining a method estimating the form of a roadsideand a method averaging the present and past correlation matrices.

In addition, Patent Document 7 describes a method which determines aweighted coefficient (or a forgetting coefficient: a constantrepresenting the degree of forgetting) in real time in order to averagethe present and past correlation matrices.

Further, an electronic scanning type radar has been used conventionallyas a radar mounted on a vehicle, which utilizes the system of an FMCW(Frequency Modulated Continuous Wave) radar, a multifrequency CW(Continuous Wave) radar, a pulse radar, and the like.

According to each of the radars mentioned above, an estimation method ofa direction of an incoming wave of an array antenna is used as atechnology for detecting a direction of an incoming wave (or a receptionwave) which is a reflection wave from a target corresponding to atransmission wave.

An example of this estimation method of a direction of an incoming waveis a null operation method (refer to Non-Patent Document 1 and 2, forinstance) known as a super-resolution (high precision) algorithm such asa beam scanning method like the Beamformer Method and the Capon Method,a linear prediction method like the Maximum Entropy Method (MEM: MaximumEntropy Method), the Minimum Norm Method, MUSIC (Multiple SignalClassification) Method, and the ESPRIT (Estimation of Signal Parametersvia Rotational Invariance Techniques) Method.

Further, the estimation of the direction of the incoming wave, used by aradar mounted on a vehicle, is conducted by a method (refer to, forexample, Patent Document 1) using solely the digital beam forming (DBF:Digital Beam Forming) of the Beamformer Method, or by a method (referto, for example, Patent Documents 2 and 3) combining the DBF and theMaximum Entropy Method in recent years in order to enhance the detectionaccuracy of the arrival direction of the reception wave (or theresolution performance of the target).

Moreover, in order to apply a super-resolution algorithm such as MUSICto a vehicle-mounted radar, methods have been developed with aninclination to simplify the processing (refer to, for example, PatentDocuments 4 and 8). These methods can be applied to a vehicle-mounteddevice which has a low processing capacity compared to normal personalcomputers.

According to the super-resolution algorithm such as MUSIC, mentionedabove, it is preferred that the direction of the incoming wave isestimated after a number of the incoming waves is estimated, in order toenhance the accuracy with which the direction is estimated.

Non-Patent Documents 1 and 2 introduce the AIC (Akaike InformationCriteria) and the MDL (Minimum Description Length) as methods toestimate the number of incoming waves based on the maximum-likelihoodapproach in statistical processing.

However, according to the estimation methods introduced in Non-PatentDocuments 1 and 2, it is necessary to collect a large amount of data andthen conduct a dispersion assessment. Therefore, it is not suitable touse these methods for a vehicle-mounted radar whose relative distance tothe target and relative velocity fluctuate rapidly.

Patent Document 8 describes a method for estimating the number ofincoming waves, necessary for computing the MUSIC spectrum, with a lightcomputation load. In other words, Patent Document 8 describes a methodwhich is an application of a threshold approach in which an eigen valueis computed, and the signal space and a noise space are estimatedindividually based on the magnitude of the eigen value.

In this case, the reception intensity of the radar declines as themeasured distance becomes larger. Therefore, the method described aboveestimates the number of incoming waves by storing and setting athreshold for each relative distance to the target, and then comparingthis threshold with the eigen value (equivalent to the receptionintensity).

In addition, there is a method (refer to Patent Documents 9, forexample) which normalizes an eigen value as one of the diagonal elementvalue of the original covariance matrix (in other words, the correlationmatrix), and then distinguishes based on a threshold value. This methodis not designed to be used for a vehicle-mounted device.

Furthermore, an estimation method which estimates the number of incomingwaves with a high degree of accuracy constantly performs a spectrumcomputation assuming that the number of incoming waves is the maximumnumber that can be received, and in the subsequent calculation ofelectronic power, unnecessary peak values are removed, and obtain afinal estimation value of the number of incoming waves (Patent Document10).

Moreover, an electronic scanning type radar has been conventionally usedas a radar mounted on a vehicle, which utilizes the system of an FMCW(Frequency Modulated Continuous Wave) radar, a multifrequency CW(Continuous Wave) radar, a pulse radar, and the like.

According to each of the radars mentioned above, an estimation method ofa direction of an incoming wave of an array antenna is used as atechnology for detecting a direction of an incoming wave (or a receptionwave) which is a reflection wave from a target corresponding to atransmission wave.

An example of this estimation method of a direction of an incoming waveis a null operation method (refer to Non-Patent Document 1 and 2, forinstance) known as a super-resolution (high precision) algorithm such asa beam scanning method like the Beamformer Method and the Capon Method,a linear prediction method like the Maximum Entropy Method (MEM: MaximumEntropy Method), the Minimum Norm Method, MUSIC (Multiple SignalClassification) Method, and the ESPRIT (Estimation of Signal Parametersvia Rotational Invariance Techniques) Method.

Further, the estimation of the direction of the incoming wave, used by aradar mounted on a vehicle, is conducted by a method (refer to, forexample, Patent Document 1) using solely the digital beam forming (DBF:Digital Beam Forming) of the Beamformer Method, or by a method (referto, for example, Patent Documents 2 and 3) combining the DBF and theMaximum Entropy Method in recent years in order to enhance the detectionaccuracy of the arrival direction of the reception wave (or theresolution performance of the target).

Moreover, in order to apply a super-resolution algorithm such as MUSICto a vehicle-mounted radar, methods have been developed with aninclination to simplify the processing (refer to, for example, PatentDocuments 4 and 8). These methods can be applied to a vehicle-mounteddevice which has a low processing capacity compared to normal personalcomputers.

According to the super-resolution algorithm such as MUSIC, mentionedabove, it is preferred that the direction of the incoming wave isestimated after a number of the incoming waves is estimated, in order toenhance the accuracy with which the direction is estimated.

Non-Patent Documents 1 and 2 introduce the AIC (Akaike InformationCriteria) and the MDL (Minimum Description Length) as methods toestimate the number of incoming waves based on the maximum-likelihoodapproach in statistical processing.

However, according to the estimation methods introduced in Non-PatentDocuments 1 and 2, it is necessary to collect a large amount of data andthen conduct a dispersion assessment. Therefore, it is not suitable touse these methods for a vehicle-mounted radar whose relative distance tothe target and relative velocity fluctuate rapidly.

Patent Document 8 describes a method for estimating the number ofincoming waves, necessary for computing the MUSIC spectrum, with a lightcomputation load. In other words, Patent Document 8 describes a methodwhich is an application of a threshold approach in which an eigen valueis computed, and the signal space and a noise space are estimatedindividually based on the magnitude of the eigen value.

In this case, the reception intensity of the radar declines as themeasured distance becomes larger. Therefore, the method described aboveestimates the number of incoming waves by storing and setting athreshold for each relative distance to the target, and then comparingthis threshold with the eigen value (which is proportional to thereception intensity).

In addition, there is a method (refer to Patent Documents 9, forexample) which normalizes an eigen value as one of the diagonal elementvalue of the original covariance matrix (in other words, the correlationmatrix), and then distinguishes based on a threshold value. This methodis not designed to be used for a vehicle-mounted device.

-   [Non-Patent Document 1] “Adaptive Signal Processing Using Array    Antennas,” Kikuma Nobuyoshi (Kagaku Gijutsu Shyuppan, 1998).-   [Non-Patent Document 2] “Adaptive Antenna Technology,” Kikuma    Nobuyoshi (Ohm Sha, 2003).-   [Patent Document 1] Japanese Unexamined Patent Application, First    Publication No. 2000-284044-   [Patent Document 2] Japanese Unexamined Patent Application, First    Publication No. 2006-275840-   [Patent Document 3] Japanese Unexamined Patent Application, First    Publication No. 2006-308542-   [Patent Document 4] Japanese Unexamined Patent Application, First    Publication No. 2007-040806-   [Patent Document 5] Japanese Unexamined Patent Application, First    Publication No. 2006-145251-   [Patent Document 6] Japanese Unexamined Patent Application, First    Publication No. 2006-242695-   [Patent Document 7] Japanese Unexamined Patent Application, First    Publication No. 2006-284182-   [Patent Document 8] Japanese Unexamined Patent Application, First    Publication No. 2006-047282-   [Patent Document 9] Japanese Unexamined Patent Application, First    Publication No. 2006-153579-   [Patent Document 10] Japanese Unexamined Patent Application, First    Publication No. 2000-121716

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, according to Patent Document 4, in the conventional averagingprocess of the correlation matrix, it is necessary to perform afrequency resolution on the past correlation matrix for all beatfrequencies. For example, when a Fourier transform is performed for 256discrete times, it is necessary to store 128 discrete frequencies. As aresult, in the conventional averaging process of the correlation matrix,there is a problem in that a large amount of memory is needed for “(thenumber of data of the correlation matrix)×(the beat frequency).” Inaddition, the beat frequency of the past correlation matrix selects thesame frequency as the beat frequency of the present target. Therefore,when the target is being followed while maintaining a constant distancein between, the data, used for detection, is averaged. Meanwhile, whenthe distance to the target fluctuates, the previous frequency may nothave a corresponding target. Therefore, the data used for detection maydeteriorate.

Furthermore, according to Patent Document 5, as a conventional averagingmethod of correlation matrices, the correlation matrix of nearby beatfrequencies are always averaged before an average is obtained with thepast correlation matrix.

Therefore, according to the conventional averaging method of correlationmatrices, it is presumed that a signal intensity is indicated as a levelof existence of the target in the frequency domain including the nearbybeat frequency. Thus, the conventional averaging method of correlationmatrices can be applied only when the discrete frequency resolution ofthe beat frequency is extremely fine. In addition, the conventionalaveraging method is executed in combination with the averaging of thecorrelation matrices for nearby beat frequencies. In this way, thearrival direction of the reception wave is not detected by using thepast correlation matrix individually.

Furthermore, according to Patent Document 6, it is presumed, as inPatent Document 5, that a method estimating the form of a roadside isperformed in the conventional averaging method of correlation matricesas well. Therefore, the arrival direction of the reception wave is notdetected by using the past correlation matrix individually. In this way,the processing is complicated.

The present invention is made considering the problems described above.One of the objects of the present invention is to provide an electronicscanning type radar device and an estimation method of a direction of areception wave which detects an arrival direction of the reception wavewith a high degree of accuracy by using a past correlation matrixindividually, and by performing a simple computation.

However, according to an estimation method of an incoming wave describedin Patent Document 8, it is necessary to store a threshold value for allof the distances for detecting the target. Thus, the necessary memorycapacity must be retained (forming a map of a table of the thresholdvalue on an ROM, for instance). In addition, this estimation method ofthe incoming wave has a problem in that the setting of the thresholdvalue and the generation of the program which performs a comparisonbetween the threshold values for each distance are cumbersome.

In addition, since the above threshold value is an absolute amount,there is a concern in that the robustness may not be enough, because itis not possible to cope with the up-and-down fluctuation of the eigenvalue due to the RCS (Radar Cross Section) of the target, a clutterwhich is a reflection from an unneeded object, and noise.

In addition, according to the estimation of the arrival wave describedin Patent Document 9, the computed eigen value is normalized by one ofthe diagonal elements of the original covariance matrix. Since thenumber of incoming waves is usually estimated, an erroneous estimate ofthe number may be computed when the incoming wave is weak. Here, “weak”indicates a signal level which is greatly below a level at which theeigen value fluctuates up and down due to the RCS of the target,clutter, and noise.

In particular, regarding a usage with a vehicle-mounted radar, there isa phenomenon called a multi-pass from a road surface (which is a type ofclutter). It is inevitable that a distance range is generated at whichthe reception wave becomes the weak signal level.

Therefore, in the distance range at which the signal level is weak, theestimation of the number of incoming wave produces an erroneous resulton the contrary.

Furthermore, according to an estimation method of the incoming wavedescribed in Patent Document 10, it is not necessary to execute aprocess estimating the number of incoming waves before the MUSICspectrum computation. However, after the spectrum computation, it isnecessary to always perform a calculation of electric power whichaccompanies an inverse matrix computation. Thus, there is a problem inthat the computation load becomes heavy.

The present invention is made considering the problems described above.One of the objects of the present invention is to provide an electronicscanning type radar device, an estimation method of a direction of areception wave, and a program estimating a direction of a reception wavewhich estimates the number of incoming waves with a high degree ofaccuracy in a robust manner when the direction of the incoming wave isestimated by performing an estimate of the incoming wave using an eigenvalue decomposition, such as the MUSIC Method or the Esprit Method.

However, according to the MUSIC Method, the accuracy of the estimate ofthe arrival direction changes, as shown below, due to the variable stepΔθ of θ regarding the evaluation function of the arrival angle.

In other words, when the variable step Δθ is increased, the amount ofcomputation decreases for the entire range in which θ varies. However,the peak direction of the evaluation function of the arrival directioncannot be detected accurately. Thus, the degree of accuracy declines.

Meanwhile, the MUSIC Method has a defect in that, although the peakdirection of the evaluation function of the arrival direction can bedetected accurately by reducing the variable step Δθ, the computationamount increases for the entire range in which θ varies.

The present invention is made considering the problems described above.One of the objects of the present invention is to provide an electronicscanning type milliwave radar device and a program estimating adirection of a reception wave, which can decrease the variable step andreduce the amount of computation for detecting an angle when an eigenexpansion such as the Music Method or the Minimum Norm Method are usedto detect a direction of an incoming wave.

Means for Solving the Problems

(1) The following measures are employed as an embodiment of the presentinvention: an electronic scanning type radar device according to anaspect of the present invention mounted on a moving body includes: atransmission unit transmitting a transmission wave; a reception unitcomprising a plurality of antennas receiving a reflection wave of thetransmission wave from a target; a beat signal generation unitgenerating a beat signal from the transmission wave and the reflectionwave; a frequency resolution processing unit frequency resolving thebeat signal into a beat frequency of a predetermined resolution numberand computing a complex number data; a target detection unit detecting apeak value from an intensity value of the beat frequency and detectingan existence of the target; a correlation matrix computation unitcomputing a correlation matrix from each of a complex number data of adetected beat frequency for which the target was detected for each ofthe antennas; a target consolidation processing unit linking the targetin a present detection cycle and a past detection cycle based on adistance and a relative velocity; a correlation matrix filtering unitgenerating an averaged correlation matrix by weighted averaging acorrelation matrix of a target in the present detection cycle and acorrelation matrix of a related target in the past detection cycle; anda direction detection unit computing an arrival direction of thereflection wave based on the averaged correlation matrix.

(2) The above electronic scanning type radar device may be configured asfollows: when the target consolidation processing unit links the targetin the present detection cycle and the past detection cycle, whether thetarget is related is detected according to whether or not a distance anda relative velocity obtained by the detected beat frequency of thepresent detection cycle is respectively included in a predetermineddistance range and a relative velocity range estimated by a distance anda relative velocity obtained by the past detection cycle.

(3) The above electronic scanning type radar device may be configured asfollows: the electronic scanning type radar device further includes amemory unit storing a distance, a relative velocity, and a correlationmatrix each corresponding to one or more past cycles of the relatedtarget, wherein the target consolidation processing unit generates anaveraged correlation matrix by weighted-averaging a correlation matrixof a target in the present detection cycle and a target in the pastdetection cycle of a plurality of temporal sequences relating to thetarget in the present detection cycle, makes a correspondence between adistance, a relative velocity, and a correlation matrix of the target inthe present detection cycle and a distance, a relative velocity, and acorrelation matrix of a related past target, and stores into the memoryunit.

(4) The above electronic scanning type radar device may be configured asfollows: the electronic scanning type radar device further includes amemory unit correspondingly storing a complex number data of a detectedbeat frequency corresponding to the related target for one or morecycles, wherein when a target of a past detection cycle related to atarget of a present detection cycle is detected, the correlation matrixcomputation unit computes the correlation matrix from the complex umberdata of the past detection cycle; and the target consolidationprocessing unit generates an averaged correlation matrixweighted-averaging a correlation matrix of a target in the presentdetection cycle and a past target related to the present target, andcorrespondingly stores a distance, a relative velocity, and a complexnumber data of a detection beat frequency of the related present targetin correspondence with a distance, a relative velocity, and a complexnumber data of the related past detection cycle.

(5) The above electronic scanning type radar device may be configured asfollows: the electronic scanning type radar device further comprising adigital beam forming unit performing a digital beam forming in adirection of a channel based on the complex number data of each antennaand detecting an existence and a direction of the target, wherein adirection of the target is detected by the digital beam forming from abeat frequency in a present detection cycle, and a correlation between atarget of a present and a past detection cycle is made based on adistance, a relative velocity, and a direction.

(6) The above electronic scanning type radar device may be configured asfollows: the electronic scanning type radar device further includes adigital beam forming unit performing a digital beam forming in adirection of a channel based on the complex number data of each antennaand detecting an existence and a direction of the target, wherein adirection of the target is detected by the digital beam forming from abeat frequency in a present detection cycle, and a correlation between atarget of a present and a past detection cycle is made based on adistance, a relative velocity, and a direction.

(7) The above electronic scanning type radar device may be configured asfollows: the electronic scanning type radar device further includes achannel deleting unit wherein, when the digital beam forming unitcomputes a spatial complex number data showing an intensity of aspectrum for each angular channel by performing a digital beam formingusing the complex number data, and an intensity of a spectrum of anadjacent angular channel exceeds a predetermined digital beam formingthreshold value in a predetermined range of a number of angularchannels, the channel deleting unit detects that a digital beam formingdetection target exists in the angular channel, and wherein, the channeldeleting unit replaces a spectrum intensity of an angular channel forwhich an existence of the digital beam forming detection target is notdetected to “0,” and outputs as a new spatial complex number data; andan inverse digital beam forming unit generating a restored complexnumber data by performing an inverse digital beam forming on the newspatial complex number data, wherein the correlation matrix computationunit computes a correlation matrix from the restored complex numberdata.

(8) The above electronic scanning type radar device may be configured asfollows: the electronic scanning type radar device further includes achannel deleting unit wherein, when the digital beam forming unitcomputes a spatial complex number data showing an intensity of aspectrum for each angular channel by performing a digital beam formingusing the complex number data, and an intensity of a spectrum of anadjacent angular channel exceeds a predetermined digital beam formingthreshold value in a predetermined range of a number of angularchannels, the channel deleting unit detects that a digital beam formingdetection target exists in the angular channel, and wherein, the channeldeleting unit replaces a spectrum intensity of an angular channel forwhich an existence of the digital beam forming detection target is notdetected to “0,” and outputs as a new spatial complex number data; andan inverse digital beam forming unit generating a restored complexnumber data by performing an inverse digital beam forming on the newspatial complex number data, wherein the correlation matrix computationunit computes a correlation matrix from the restored complex numberdata.

(9) The above electronic scanning type radar device may be configured asfollows: when the channel deleting unit detects a plurality of digitalbeam forming detection targets, a spectrum is divided for each angularchannel range corresponding to each digital beam forming detectiontarget, thereby generating a spatial complex number data for eachdigital beam forming detection target, the inverse digital beam formingunit generates a restored complex number data for each digital beamforming detection target by respectively performing an inverse digitalbeam forming on a spatial complex number data for each of the digitalbeam forming detection target, and the correlation matrix computationunit computes a correlation matrix for each digital beam formingdetection target from a restored complex number data of each of thedigital beam forming detection targets.

(10) The above electronic scanning type radar device may be configuredas follows: when the channel deleting unit detects a plurality ofdigital beam forming detection targets, a spectrum is divided for eachangular channel range corresponding to each digital beam formingdetection target, thereby generating a spatial complex number data foreach digital beam forming detection target, the inverse digital beamforming unit generates a restored complex number data for each digitalbeam forming detection target by respectively performing an inversedigital beam forming on a spatial complex number data for each of thedigital beam forming detection target, and the correlation matrixcomputation unit computes a correlation matrix for each digital beamforming detection target from a restored complex number data of each ofthe digital beam forming detection targets.

(11) The above electronic scanning type radar device may be configuredas follows: the correlation matrix filtering unit varies a weightedcoefficient, used during a weighted-averaging, with respect to each ofthe targets corresponding to the relative velocity.

(12) The above electronic scanning type radar device may be configuredas follows: when a change in a position of the target in a lateraldirection obtained from a direction and a distance in a past and apresent exceeds a predetermined range, the correlation matrix filteringunit varies a weighting coefficient, used during a weighted-averaging,with respect to each of the target.

(13) The above electronic scanning type radar device may be configuredas follows: a number of past cycles used when the target consolidationprocessing unit computes an average is varied corresponding to therelative velocity.

(14) A reception wave direction estimation method according to an aspectof the present invention by an electronic scanning type radar devicemounted on a moving body includes: a transmission process transmitting atransmission wave from a transmission unit; a reception process in whicha reception unit comprising a plurality of antennas receives areflection wave of the transmission wave from a target; a beat signalgeneration process in which a beat signal generation unit generates abeat signal from the transmission wave and the reflection wave; afrequency resolution processing step in which a frequency resolutionprocessing unit frequency resolves the beat signal into a beat frequencyof a predetermined resolution number and computes a complex number data;a target detecting process in which a target detection unit detects apeak value from an intensity value of the beat frequency and detects anexistence of the target; a correlation matrix computing process in whicha correlation matrix computation unit computes a correlation matrix fromeach of a complex number data of a detected beat frequency for which thetarget was detected for each of the antennas; a target consolidationprocessing step in which a target consolidation processing unit linksthe target in a present detection cycle and a past detection cycle basedon a distance and a relative velocity; a correlation matrix filteringprocess in which a correlation matrix filtering unit generates anaveraged correlation matrix by weighted averaging a correlation matrixof a target in the present detection cycle and a correlation matrix of arelated target in the past detection cycle; and a direction detectionprocess in which a direction detection unit computes an arrivaldirection of a reception wave based on the averaged correlation matrix.

(15) A reception wave direction estimation program according to anaspect of the present invention is a program for an electronic scanningtype radar device mounted on a moving body to make a computer control anoperation of a reception wave direction estimation. The reception wavedirection estimation program according to an aspect of the presentinvention includes: a transmission process transmitting a transmissionwave from a transmission unit; a reception process in which a receptionunit makes a plurality of antennas receive a reflection wave of thetransmission wave from a target; a beat signal generation process inwhich a beat signal generation unit generates a beat signal from thetransmission wave and the reflection wave; a frequency resolutionprocessing step in which a frequency resolution processing unitfrequency resolves the beat signal into a beat frequency of apredetermined resolution number and computes a complex number data; atarget detecting process in which a target detection unit detects a peakvalue from an intensity value of the beat frequency and detects anexistence of the target; a correlation matrix computing process in whicha correlation matrix computation unit computes a correlation matrix fromeach of a complex number data of a detected beat frequency for which thetarget was detected for each of the antennas; a target consolidationprocessing step in which a target consolidation processing unit linksthe target in a present detection cycle and a past detection cycle basedon a distance and a relative value; a correlation matrix filteringprocess in which a correlation matrix filtering unit generates anaveraged correlation matrix by weighted averaging a correlation matrixof a target in the present detection cycle and a correlation matrix of arelated target in the past detection cycle; and a direction detectionprocess in which a direction detection unit computes an arrivaldirection of a reception wave based on the averaged correlation matrix.

(16) An electronic scanning type radar device according to an aspect ofthe present invention mounted on a moving body includes: a transmissionunit transmitting a transmission wave; a reception unit comprising aplurality of antennas receiving an incoming wave, the incoming wavebeing a reflection wave of the transmission wave from a target; a beatsignal generation unit generating a beat signal comprising a frequencyof a difference between the transmission wave and the reflection wave; afrequency resolution processing unit frequency resolving the beat signalinto a beat frequency of a predetermined resolution number inchronological order and computing a complex number data; a peakdetection unit detecting a peak value from an intensity value of each ofthe beat frequency and detecting an existence of a target; a correlationmatrix computation unit computing a correlation matrix from each of acomplex number data of a detected beat frequency for which the targetwas detected for each of the antennas; an eigen value computation unitcomputing an eigen value from a correlation matrix; a comparison unitcomparing an eigen value obtained by normalizing, and a predeterminedthreshold value; a determination unit determining a number of an eigenvalue of a numeric value, among an eigen value corresponding to a beatfrequency for which a target was detected, the numeric value exceedingthe threshold value, as a number of the incoming waves.

(17) The above electronic scanning type radar device may be configuredas follows: the eigen value computation unit, concerning an eigen valuehaving a maximum value among the computed eigen value, normalizes alleigen values by performing a division, and wherein the comparison unitcompares the normalized eigen value and the predetermined thresholdvalue.

(18) The above electronic scanning type radar device may be configuredas follows: the eigen value computation unit, by a maximum value elementof the correlation matrix, divides all of the element of the correlationmatrix, and computes an eigen value based on a correlation matrix whoseelement is normalized, and wherein the comparison unit compares theeigen value with the predetermined threshold value.

(19) The above electronic scanning type radar device may be configuredas follows: the determination unit compares a predetermined maximumeigen value threshold value and a maximum eigen value among an obtainedeigen value, and, when the maximum eigen value exceeds the predeterminedmaximum eigen value threshold value, the determination unit finds thatthe eigen value is of an effective reception level, and performs anestimation of a number of an incoming wave.

(20) The above electronic scanning type radar device may be configuredas follows: the eigen value computation unit divides all element of thecorrelation matrix with an element having a maximum value among adiagonal element of the correlation matrix, computes an eigen valuebased on a correlation matrix whose elements are normalized, and whereinthe comparison unit compares the eigen value and the predeterminedthreshold value.

(21) The above electronic scanning type radar device may be configuredas follows: the electronic scanning type radar device further includes apeak value comparison unit comparing the peak value with a predeterminedeffective reception level, wherein when the peak value exceeds thepredetermined effective reception level, the determination unit findsthat an eigen value is of an effective determination level, andestimates a number of a incoming wave.

(22) The above electronic scanning type radar device may be configuredas follows: the determination unit compares a predetermined maximumcorrelation matrix diagonal element threshold value and a maximum valueof a diagonal element of the correlation matrix which was obtained, andwhen the maximum value of the diagonal element exceeds the maximumcorrelation matrix diagonal element threshold, the determination unitfinds that an eigen value is of an effective reception level, andestimates a number of an incoming wave.

(23) The above electronic scanning type radar device may be configuredas follows: the peak detection unit comprises a digital beam formingunit which performs a digital beam forming in a direction of a channelbased on the complex number data for each of the antennas, and detectsan existence of the target.

(24) The above electronic scanning type radar device may be configuredas follows: the electronic scanning type radar device further includes achannel deleting unit wherein, when the digital beam forming unitcomputes a spatial complex number data showing an intensity of aspectrum for each angular channel by performing a digital beam formingusing the complex number data, and an intensity of a spectrum of anadjacent angular channel exceeds a predetermined digital beam formingthreshold value in a predetermined range of a number of angularchannels, the channel deleting unit detects an existence of a target,and wherein, the channel deleting unit replaces a spectrum intensity ofan angular channel for which the existence of the target is not detectedto “0,” and outputs a new spatial complex number data; and an inversedigital beam forming unit generating a restored complex number data byperforming an inverse digital beam forming on the new spatial complexnumber data, wherein the correlation matrix computation unit computes acorrelation matrix from the restored complex number data.

(25) The above electronic scanning type radar device may be configuredas follows: the peak detection unit converts an added value of a complexnumber data of all of the antennas to a frequency spectrum, and detectsa target based on a peak value of the frequency spectrum.

(26) A reception wave direction estimation method by an electronicscanning type radar device according to an aspect of the presentinvention mounted on a moving body includes: a transmission processtransmitting a transmission wave from a transmission unit; a receptionprocess in which a reception unit comprising a plurality of antennasreceives a reflection wave of the transmission wave from a target; abeat signal generation process in which a beat signal generation unitgenerates a beat signal comprising a frequency of a difference betweenthe transmission wave and the reflection wave; a frequency resolutionprocessing step in which a frequency resolution processing unitfrequency resolves the beat signal into a beat frequency of apredetermined resolution number and computes a complex number data inchronological order; a peak detection process in which a peak detectionunit detects a peak value from an intensity value of each of the beatfrequency and detecting an existence of the target; a correlation matrixcomputing process in which a correlation matrix computation unitcomputes a correlation matrix from each of a complex number data of adetected beat frequency for which the target was detected for each ofthe antennas; an eigen value computation process in which an eigen valuecomputation unit computes an eigen value from a correlation matrix; acomparison process in which a comparison unit compares an eigen valueobtained by normalizing, and a predetermined threshold value; and adetermination process in which the determination unit determines anumber of an eigen value of a numeric value, among an eigen valuecorresponding to a beat frequency for which a target was detected, thenumeric value exceeding the threshold value, as a number of the incomingwaves.

(27) A reception wave direction estimation program according to anaspect of the present invention is a program for an electronic scanningtype radar device mounted on a moving body to make a computer control anoperation of a reception wave direction estimation. The reception wavedirection estimation program according to an aspect of the presentinvention includes a transmission process transmitting a transmissionwave from a transmission unit; a reception process in which a receptionunit comprising a plurality of antennas receives an incoming wave, theincoming wave being a reflection wave of the transmission wave from atarget; a beat signal generation process in which a beat signalgeneration unit generates a beat signal comprising a frequency of adifference of the transmission wave and the reflection wave; a frequencyresolution processing step in which a frequency resolution processingunit frequency resolves the beat signal into a beat frequency of apredetermined resolution number and computes a complex number data inchronological order; a peak detection process in which a peak detectionunit detects a peak value from an intensity value of each of the beatfrequency and detects an existence of the target; a correlation matrixcomputing process in which a correlation matrix computation unitcomputes a correlation matrix from each of a complex number data of adetected beat frequency for which the target was detected for each ofthe antennas; an eigen value computation process in which an eigen valuecomputation unit computes an eigen value from a correlation matrix; acomparison process in which a comparison unit compares an eigen valueobtained by normalizing, and a predetermined threshold value; and adetermination process in which the determination unit determines anumber of an eigen value of a numeric value, among an eigen valuecorresponding to a beat frequency for which a target was detected, thenumeric value exceeding the threshold value, as a number of the incomingwaves.

(28) An electronic scanning type radar device according to an aspect ofthe present invention mounted on a moving body includes: a transmissionunit transmitting a transmission wave; a reception unit comprising aplurality of antennas receiving an incoming wave, the incoming wavebeing a reflection wave of the transmission wave from a target; a beatsignal generation unit generating a beat signal comprising a frequencyof a difference between the transmission wave and the reflection wave; afrequency resolution processing unit frequency resolving the beat signalinto a beat frequency of a predetermined resolution number and computinga complex number data in chronological order; an angular range settingunit computing an angular range in which a target exists based on thecomplex number data; and a direction detection unit computing an angularspectrum in the angular range.

(29) The above electronic scanning type radar device may be configuredas follows: the angular range setting unit includes a digital beamforming unit performing a digital beam forming on the complex numberdata in an alignment direction of an antenna, computing an intensity ofa spectrum for each angular channel, detecting an existence of a target,and obtaining information on a direction; and a range detection unitsetting, based on a data of a frequency axis for which the target existsand based on directional information, an angular range for which anangular spectrum is computed.

(30) The above electronic scanning type radar device may be configuredas follows: the angular range setting unit further includes: a channeldeleting unit performing a division into a plurality of groups accordingto whether a target exists in a direction of an angular channel based ona spectrum intensity for each of an angular channel computed by thedigital beam forming processing unit, the channel deleting unit furthersetting a spectrum intensity of an angular channel for which a targetdoes not exist to “0”; and an inverse digital beam forming processingunit performing an inverse digital beam forming on a spectrum intensityfor each of the angular channels and restoring a complex number data foreach antenna, and outputting as a restored complex number data, whereinthe range detection unit sets an angular range for which an angularspectrum is computed, based on the restored complex number data,information on a direction in which a target exists, and an estimationvalue of a number of a reception wave.

(31) The above electronic scanning type radar device may be configuredas follows: the angular range setting unit further includes a channeldeleting unit performing a division into a plurality of groups accordingto whether a target exists in a direction of an angular channel based ona spectrum intensity for each of an angular channel computed by thedigital beam forming processing unit, the channel deleting unit furthersetting a spectrum intensity of an angular channel for which a targetdoes not exist to “0”; and an inverse digital beam forming processingunit performing an inverse digital beam forming on a spectrum intensityfor each of the angular channels and restoring a complex number data foreach antenna, and outputting as a restored complex number data, whereinthe direction detection unit computes a root corresponding to an angle,based on the restored complex number data and an estimation value of anumber of a reception wave.

(32) The above electronic scanning type radar device may be configuredas follows: the angular range setting unit further includes a channeldeleting unit performing a division into a plurality of groups accordingto whether a target exists in a direction of an angular channel based ona spectrum intensity for each of an angular channel computed by thedigital beam forming processing unit, the channel deleting unit furthersetting a spectrum intensity of an angular channel for which a targetdoes not exist to “0”; an inverse digital beam forming processing unitperforming an inverse digital beam forming on a spectrum intensity foreach of the angular channels and restoring a complex number data foreach antenna, and outputting as a restored complex number data; and amemory unit storing information on a direction of each of a target in apast direction detection cycle, wherein the range detection unit sets anangular range for which an angular spectrum is computed, based on therestored complex number data, information on a direction of a pastdirection detection cycle stored in the memory unit, and an estimationvalue of a number of a reception wave.

(33) The above electronic scanning type radar device may be configuredas follows: an estimation value of a number of a reception wave is aneigen value.

(34) The above electronic scanning type radar device may be configuredas follows: the angular range setting unit includes: a peak detectionunit detecting an existence of a target based on a peak value of anintensity of a frequency axis; a memory unit storing information on adirection of each of a target in a past direction detection cycle; and arange detection unit limiting the angular range based on an informationon a direction of a past direction detection cycle stored in the memoryunit, and writing in an obtained angular range into the memory unit.

(35) A reception wave direction estimation method by an electronicscanning type radar device according to an aspect of the presentinvention mounted on a moving body includes: a transmission processtransmitting a transmission wave from a transmission unit; a receptionprocess in which a reception unit comprising a plurality of antennasreceiving an incoming wave, the incoming wave being a reflection wave ofthe transmission wave from a target; a beat signal generation process inwhich a beat signal generation unit generates a beat signal comprising afrequency of a difference between the transmission wave and thereflection wave; a frequency resolution processing step in which afrequency resolution processing unit frequency resolves the beat signalinto a beat frequency of a predetermined resolution number and computesa complex number data in chronological order; an angular range settingprocess in which an angular range setting unit computes an angular rangein which a target exists based on the complex number data; and adirection detection process in which a direction detection unit computesan angular spectrum in the angular range.

(36) A reception wave direction estimation program according to anaspect of the present invention is a program for an electronic scanningtype radar device mounted on a moving body to make a computer control anoperation of a reception wave direction estimation. The reception wavedirection estimation program according to an aspect of the presentinvention includes a transmission process transmitting a transmissionwave from a transmission unit; a reception process in which a receptionunit makes a plurality of antennas receive an incoming wave, theincoming wave being a reflection wave of the transmission wave from atarget; a beat signal generation process in which a beat signalgeneration unit generates a beat signal comprising a frequency of adifference between the transmission wave and the reflection wave; afrequency resolution processing step in which a frequency resolutionprocessing unit frequency resolves the beat signal into a beat frequencyof a predetermined resolution number and computes a complex number datain chronological order; an angular range setting process in which anangular range setting unit computes an angular range in which a targetexists based on the complex number data; and a direction detectionprocess in which a direction detection unit computes an angular spectrumin the angular range.

Effects of the Invention

According to the embodiment described in (1) above, the targetconsolidation processing unit relates the same target in the present andin the past to one another. Then, the target consolidation processingunit performs an averaging process of the correlation matrix. Therefore,regardless of the fluctuation of the distance to the target, the eigenvalue computation in the subsequent direction detection process and thespectrum computation (such as MUSIC) can be performed accurately. Thus,compared to the instance in which the computation is performed using thecorrelation matrix of only the present time, it is possible to enhancethe recognition performance of the final distance and direction of thetarget.

In addition, according to the embodiment described in (1) above, aplurality of correlation matrices or complex number data are stored foreach target. Since all of these are used to perform the averagingprocess, the recognition performance of the final distance and directionof the target can be further enhanced regardless of the fluctuation inthe distance to the target.

In addition, according to the embodiment described in (13) above, thenumber of detection cycles of the correlation matrix used to average thecorrelation matrix are altered optionally for each target based on therelative velocity with respect to the target. Thus, when the distance tothe target is fluctuating, the number of detection cycles is reduced.Meanwhile, when the distance to the target is stable, the number ofdetection cycles is increased. As a result, the correlation matrixfiltering unit can have an appropriate filtering characteristic based onthe condition of the relative velocity with respect to each target.Consequently, the recognition performance of the final distance anddirection of the target can be further enhanced regardless of thefluctuation in the distance to the target.

In addition, according to the embodiment described in (11) above, theaveraging weight coefficient used to average the correlation matrix canbe varied for each target based on the relative velocity with respect tothe target. As a result, the correlation matrix filtering unit can havean appropriate filtering characteristic based on the condition of therelative velocity with respect to each target. Consequently, therecognition performance of the final distance and direction of thetarget can be further enhanced.

In addition, according to the embodiment described in (11) above, whenthe amount of change of the lateral position, obtained by the directionand the distance in the past and in the present, exceeds a predeterminedrange, the weight coefficient used to compute a weighted average isaltered according to each target. In other words, the correlation matrixfiltering unit can have an appropriate filtering characteristic suchthat the number of past cycles to be averaged is reduced, or, theweighting coefficients are made variable and the number of linkage isthus substantively reduced. Consequently, the recognition performance ofthe final distance and direction of the target can be further enhanced.

In addition, according to the embodiment described in (3) above, thecomplex number data of the target frequency is stored. As a result, thepast data stored in the memory equals, for each target, the number ofchannels of the plurality of original antennas×2 (the complex numberdata of the real part and the imaginary part). Therefore, compared tothe case in which the storing is made simply by the correlation matrix,the memory size can be reduced.

In addition, according to the embodiment described in (5) above, a DBFunit is provided, which detects a direction by DBF from the beatfrequency which has undergone a frequency resolution. Thus, linkage ismade not only for the prediction range from the distance and therelative velocity, but also for the range of the direction. Therefore,the past and present correlation matrices can be linked with moreaccuracy.

In addition, according to the embodiment described in (7) above, thespectrum is divided for each angle channel range corresponding to theDBF detection target. At the same time, each special complex number datais generated. The IDBF unit computes a correlation matrix for each DBFdetection target from a regenerated complex number data which isobtained by performing a reverse DBF on the respective space complexnumber data for each of the DBF detection target. As a result, thecorrelation matrix, used when performing an eigen value calculation,includes only the element of the incoming reception wave for each DBFdetection target. Thus even if the number of incoming reception waves isgreater than or equal to the number of reception antennas and subarrays,the recognition performance of the direction and the distance can bereduced and be made more accurate without making an error in the eigenvalue calculation for each DBF detection target.

In addition, according to the embodiment described in (16) above, thenumber of eigen values which exceed a predetermined threshold value isoutput as the number of incoming waves, in regards to the eigen valueobtained by normalization. Thus, regardless of the beat frequency (i.e.,the distance to the target) for which a target exists, a threshold valuecan be set for the eigen value of all beat frequency which underwent aFourier transform, without setting a threshold for each beat frequencyas was done conventionally. Hence, the number of eigen values thatexceeded the threshold value can be an estimate of the number ofincoming waves. In this way, it is not necessary to set a thresholdvalue for each beat frequency, as was done conventionally, in order tomake a comparison with the eigen value. Therefore, the memory size canbe reduced. Moreover, since the computation is a simple one comparingthe eigen value with the threshold value, it is possible to reduce theprocessing time of computing the number of incoming waves.

In addition, according to the embodiment described in (16) above, adetermination is made comparing the eigen value, computed bynormalization, and the threshold value. Thus, the robustness can beenhanced in response to the fluctuation of the overall eigen values dueto the RCS of the target, clutter, and noise.

In addition, according to the embodiment described in (16) above, theexistence of the target is detected from the peak value of the spectrum(the peak value of the added value of the spectrum for each receptionantenna or the DBF) at the frequency point (the beat frequency value)for the frequency axis after the frequency conversion. Thus, the processafter the formation of the correlation matrix is not executed withrespect to the beat frequency value with a low peak value. Therefore,even if the eigen value exceeds the threshold value, an erroneousestimation of the incoming wave is prevented when the incoming wave froma target is weak due to a multi-pass from the road surface.

In addition, according to the embodiment described in (24) above, a DBFis performed on the beat frequency value for which a target exists. Whenthe spectrum is lower than the predetermined value, an IDBF (an inverseDBF) is performed by setting the spectrum corresponding to the anglechannel to “0.” Further, when the correlation matrix is computed usingthe regenerated complex number data in the direction of the receptionantenna, an eigen value within only the range divided for each target inthe DBF is obtained, which is equivalent to receiving only the divided,incoming wave. Thus, even if the number of incoming waves is greaterthan the number of reception antennas, an erroneous estimation is notmade in the eigen value calculation.

In addition, according to the embodiment described in (19) above, thedetermining unit performs an estimation process of the number ofincoming waves only when the value of the maximum eigen value among theobtained eigen values exceeds the predetermined maximum eigen valuethreshold. Thus, even in an embodiment configured so that the even valueis computed from the correlation matrix in the overall frequency pointor in a range of the specific frequency point, without using thedetection result of the target, obtained from the peak value of thespectrum based on the frequency point after the frequency resolution, anerroneous estimation is not made when the incoming wave from the targetis weak due to a multi-pass from the road surface.

In addition, according to the embodiment described in (20) above,normalization is made by dividing all elements by the maximum value ofthe elements of the correlation matrix. Further, the eigen value iscomputed based on the normalized correlation matrix. As a result, theaccuracy of the floating-point calculation, which is executed when theeigen value is computed, can be enhanced. In addition, it is possible toreduce the number of computations necessary for the conversion of thearithmetic algorithm (such as the Jacobi Method and the QR Method) ofthe eigen value and the eigen vector. In this way, it is possible tospeed up the computation of the eigen value and the eigen vector.

In addition, according to the embodiment described in (28) above, thedirection can be detected in a generalized manner by using the anglerange outputted by the angle range setting unit. Thus, when the anglespectrum is computed by the direction detection unit, the angle spectrumof the above specific angle range corresponding to the detecteddirection of the target is computed with priority. Therefore, it ispossible to reduce the variable step Δθ. It is also possible to make theresolution performance of the computation more minute. Thus, the arrivaldirection of the incoming wave can be computed with more accuracy. As aresult, according to an embodiment of the present invention, in thespectrum computation operation, which has a heavy processing load nextto eigen value calculations, the range of the angle which is computed islimited and narrowed, thus reducing the load, and thereby enhancing theresolution performance of the calculation.

In addition, according to the embodiment described in (32) above, byreferring to the direction of the target in the past cycle recorded inthe memory, the direction of the target in the past cycle can bechecked. Thus, when the direction detection unit, for example, computesthe angle spectrum, the angle spectrum can be computed with priority inthe specific angle range corresponding to the direction of the pastcycle. Therefore, it is possible to reduce the variable step Δθ and makethe resolution performance of the computation more minute. In this way,the direction of the arrival direction of the incoming wave can becomputed with more accuracy.

In addition, according to the embodiment described in (30) above, a DBFof the beat frequency for which a target exists is performed, anunnecessary angle channel is deleted (making the spectrum intensity“0”), an IDBF is performed after the deletion, a correlation matrix isgenerated in the direction of the reception channel by the regeneratedcomplex data, and the eigen value computation is executed. As a result,this is equivalent to receiving only the divided incoming wave. Thus,even if the number of received incoming waves is large compared to thenumber of reception antennas, it is possible to compute the arrivaldirection of the incoming wave without making an error in the eigenvalue computation.

In addition, according to the embodiment described in (31) above, theentire detectable range of angles is divided into a plurality of angleranges. Thus, it is possible to estimate the maximum value of theactually used number of arrival waves (the number of targets) if withinthe divided narrow angle range. Therefore, a spectrum estimation can beconducted according to the predetermined fixed number of arrival waves.

In addition, according to the embodiment described in (30) above, when aplurality of target clusters exist, and when each of the target clusteris positioned in different directions, a plurality of angle ranges areset corresponding to a plurality of incoming waves. Thus, in each anglerange, the separation and the direction of the incoming wave can beestimated with greater accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to a first embodiment ofthe present invention.

FIG. 2A is a conceptual diagram describing a generation of a beat signalin an ascending region and a descending region of a triangular wave by atransmission wave and a reception wave.

FIG. 2B is a conceptual diagram describing a generation of a beat signalin an ascending region and a descending region of a triangular wave by atransmission wave and a reception wave.

FIG. 3 is a conceptual diagram describing a reception wave by areception antenna.

FIG. 4 is a graph showing a beat frequency (horizontal axis) and itspeak value (vertical axis) which is a result of a frequency resolutionof a beat signal.

FIG. 5 is a table showing a matrix of a beat frequency in an ascendingregion and a descending region at a combination unit 24, an intersectionof the matrix, i.e., a distance and a relative velocity according to acombination of a beat frequency in an ascending region and a descendingregion.

FIG. 6 is a table showing a distance and a relative velocity for eachtarget in a present detection cycle.

FIG. 7 is a flowchart describing a MUSIC operation.

FIG. 8A is a flowchart showing a substep executed in step S103 of theflowchart shown in FIG. 7.

FIG. 8B is a flowchart showing a substep executed in step S103 of theflowchart shown in FIG. 7.

FIG. 9 is a conceptual diagram describing a process executed when aspatial average of a correlation matrix is computed.

FIG. 10 is a conceptual diagram used when a correlation is made betweena present detection cycle and a past detection cycle, and shows aconfiguration of a table in which a correlation matrix is enteredcorresponding to a distance and a relative velocity of the pastdetection cycle.

FIG. 11 is a flowchart showing a substep of step S103_3 in FIG. 8A.

FIG. 12 is a conceptual diagram describing an averaging operation of apresent detection cycle and a past (multiple) detection cycle(s).

FIG. 13 is a flowchart showing a substep of step S103_1 in FIG. 8B.

FIG. 14A is a conceptual diagram describing a number of detection cyclescorresponding to a detection cycle.

FIG. 14B is a conceptual diagram describing a number of detection cyclescorresponding to a detection cycle.

FIG. 15 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to a variation of thefirst embodiment of the present invention.

FIG. 16 is a flowchart showing a substep of step S103_3 in FIG. 8A.

FIG. 17 is a flowchart showing a substep of step S103_1 in FIG. 8B.

FIG. 18 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to a second embodimentof the present invention.

FIG. 19 is a conceptual diagram used when a correlation is made betweena present detection cycle and a past detection cycle, and shows aconfiguration of a table in which a correlation matrix is enteredcorresponding to a distance, a longitudinal position, a lateralposition, and a relative velocity of the past detection cycle.

FIG. 20 is a table showing a correspondence between each angle of eachtarget in a present detection cycle and frequency point.

FIG. 21 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to a third embodiment ofthe present invention.

FIG. 22 is a table showing a distance, a longitudinal position, alateral position, and a relative velocity for each target in a presentdetection cycle.

FIG. 23 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to a fourth embodimentof the present invention.

FIG. 24A is a conceptual diagram describing a processing of a spectrumintensity for each angle channel.

FIG. 24B is a conceptual diagram describing a processing of a spectrumintensity for each angle channel.

FIG. 24C is a conceptual diagram describing a processing of a spectrumintensity for each angle channel.

FIG. 25A is a conceptual diagram describing a processing of a spectrumintensity for each angle channel.

FIG. 25B is a conceptual diagram describing a processing of a spectrumintensity for each angle channel.

FIG. 25C is a conceptual diagram describing a processing of a spectrumintensity for each angle channel.

FIG. 26 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to a fifth embodiment ofthe present invention.

FIG. 27A is a conceptual diagram describing a generation of a beatsignal in an ascending region and a descending region of a triangularwave by a transmission wave and a reception wave.

FIG. 27B is a conceptual diagram describing a generation of a beatsignal in an ascending region and a descending region of a triangularwave by a transmission wave and a reception wave.

FIG. 28 is a conceptual diagram describing a reception wave by areception antenna.

FIG. 29 is a graph showing a beat frequency (horizontal axis) and itspeak value (vertical axis) which is a result of a frequency resolutionof a beat signal.

FIG. 30 is a flowchart describing a MUSIC operation.

FIG. 31A is a flowchart showing a substep executed in step S1103 of theflowchart shown in FIG. 30.

FIG. 31B is a flowchart showing a substep executed in step S1103 of theflowchart shown in FIG. 30.

FIG. 32 is a conceptual diagram describing a process executed when aspatial average of a correlation matrix is computed.

FIG. 33 is a flowchart describing in detail a process estimating anumber of incoming waves, executed in step S1105 shown in FIG. 30.

FIG. 34 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S1105 shown in FIG. 30.

FIG. 35 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S1105 shown in FIG. 30.

FIG. 36 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S1105 shown in FIG. 30.

FIG. 37 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S1105 shown in FIG. 30.

FIG. 38A is a graph showing a distance when a number of incoming wave is1, and also showing a correspondence between an eigen value and eachdistance.

FIG. 38B is a graph showing a distance when a number of incoming wave is1, also showing a correspondence between an eigen value and eachdistance.

FIG. 38C is a table showing an eigen value λx when a number of incomingwave is 1 at distance 100 (m), also showing a difference in valuesbetween an eigen value λ1 in a signal space and an eigen value in anotherwise noise space.

FIG. 39A is a graph showing a distance when a number of incoming wavesis 2, also showing a correspondence between an eigen value and eachdistance.

FIG. 39B is a graph showing a distance when a number of incoming wavesis 2, also showing a correspondence between an eigen value and eachdistance.

FIG. 40 is a block diagram showing an example of a configuration of asignal processing unit 120 of an electronic scanning type radar deviceaccording to a sixth embodiment of the present invention.

FIG. 41A is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 41B is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 41C is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 42A is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 42B is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 42C is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 43 is a block diagram showing an example of a configuration of asignal processing unit 120 of an electronic scanning type radar deviceaccording to a seventh embodiment of the present invention.

FIG. 44 is a block diagram showing an example of a configuration of anelectronic scanning type radar device according to an embodiment of thepresent invention.

FIG. 45 is a block diagram showing an example of a configuration of asignal processing unit 220 of an electronic scanning type radar deviceaccording to an eighth embodiment of the present invention.

FIG. 46A is a conceptual diagram describing a generation of a beatsignal in an ascending region and a descending region of a triangularwave by a transmission wave and a reception wave.

FIG. 46B is a conceptual diagram describing a generation of a beatsignal in an ascending region and a descending region of a triangularwave by a transmission wave and a reception wave.

FIG. 47 is a conceptual diagram describing a reception wave by areception antenna.

FIG. 48 is a graph showing a beat frequency (horizontal axis) and itspeak value (vertical axis) which is a result of a frequency resolutionof a beat signal.

FIG. 49A is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 49B is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 49C is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 50A is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 50B is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 50C is a graph describing a focusing process of an angle range forcomputing a MUSIC spectrum using a DBF process.

FIG. 51 is a flowchart explaining a MUSIC process.

FIG. 52A is a flowchart showing a substep executed in step S2103 in theflowchart shown in FIG. 51.

FIG. 52B is a flowchart showing a substep executed in step S2103 in theflowchart shown in FIG. 51.

FIG. 53 is a conceptual diagram describing a process executed when aspatial average of a correlation matrix is computed.

FIG. 54 is a flowchart describing in detail a process estimating anumber of incoming waves, executed in step S2105 shown in FIG. 51.

FIG. 55 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S2105 shown in FIG. 51.

FIG. 56 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S2105 shown in FIG. 51.

FIG. 57 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S2105 shown in FIG. 51.

FIG. 58 is a flowchart describing in detail another process estimating anumber of incoming waves, executed in step S2105 shown in FIG. 51.

FIG. 59A is a graph showing a distance when a number of incoming wave is1, and also showing a correspondence between an eigen value and eachdistance.

FIG. 59B is a graph showing a distance when a number of incoming wave is1, and also showing a correspondence between an eigen value and eachdistance.

FIG. 59C is a table showing an eigen value λx when a number of incomingwave is 1 at distance 100 (m), also showing a difference in valuesbetween an eigen value λ1 in a signal space and an eigen value in anotherwise noise space.

FIG. 60A is a graph showing a distance when a number of incoming wavesis 2, also showing a correspondence between an eigen value and eachdistance.

FIG. 60B is a graph showing a distance when a number of incoming wavesis 2, also showing a correspondence between an eigen value and eachdistance.

FIG. 61 is a block diagram showing an example of a configuration of asignal processing unit 220 of an electronic scanning type radar deviceaccording to a ninth embodiment of the present invention.

FIG. 62 is a conceptual diagram showing an electronic scanning typeradar device and a computer mounted on a moving body, the electronicscanning type radar device transmitting a transmission wave, and theelectronic scanning type radar device receiving a reflection wave causedby the transmission wave reflecting from a target.

DESCRIPTION OF THE REFERENCE SYMBOLS

11˜1 n . . . Reception antenna, 61˜6 n . . . Mixer (Beat signalgeneration unit), 3 . . . Transmission antenna, 4 . . . Distributor,51˜5 n . . . Filter, 6 . . . SW, 7 . . . ADC, 8 . . . Control unit, 9 .. . Triangular wave generation unit, 10 . . . VCO, 20 . . . Signalprocessing unit, 21 . . . Memory (Memory unit), 22 . . . Frequencyresolution processing unit, 23 . . . Peak detection unit, 24 . . . Peakcombination unit, 25 . . . Distance detection unit, 26 . . . Velocitydetection unit, 27, 27B . . . Pair confirmation unit, 28 . . .Correlation matrix computation unit, 29 . . . Correlation matrixfiltering unit, 30 . . . Direction detection unit, 31, 31B . . . Targetconfirmation unit, 32, 32B . . . Target consolidation processing unit,40 . . . DBF processing unit, 41 . . . Ch Deleting Unit, 42, 43 . . .IDBF processing unit, 111˜11 n . . . Reception antenna, 161˜16 n . . .Mixer (Beat signal generation unit), 103 . . . Transmission antenna, 104. . . Distributor, 151˜15 n . . . Filter, 106 . . . SW, 107 . . . ADC,108 . . . Control unit, 109 . . . Triangular wave generation unit, 110 .. . VCO, 120 . . . Signal processing unit, 121 . . . Memory (Memoryunit), 122 . . . Frequency resolution processing unit, 123 . . . Peakdetection unit, 124 . . . Peak combination unit, 125 . . . Distancedetection unit, 126 . . . Velocity detection unit, 127, 127B . . . Pairconfirmation unit, 128 . . . Correlation matrix computation unit, 130 .. . Direction detection unit, 131 . . . Eigen value computation unit,132 . . . Determination unit, 133 . . . DBF processing unit, 134 . . .Ch Deleting Unit, 135 . . . IDBF processing unit, 211˜21 n . . .Reception antenna, 261˜26 n . . . Mixer (Beat signal generation unit),203 . . . Transmission antenna, 204 . . . Distributor, 251˜25 n . . .Filter, 206 . . . SW, 207 . . . ADC, 208 . . . Control unit, 209 . . .Triangular wave generation unit, 210 . . . VCO, 220 . . . Signalprocessing unit, 221 . . . Memory (Memory unit), 222 . . . Frequencyresolution processing unit, 223 . . . Peak detection unit, 224 . . .Peak combination unit, 225 . . . Distance detection unit, 226 . . .Velocity detection unit, 227, 227B . . . Pair confirmation unit, 228 . .. Correlation matrix computation unit, 230 . . . Direction detectionunit, 231 . . . Eigen value computation unit, 232 . . . Determinationunit, 233 . . . DBF processing unit, 234 . . . Ch Deleting Unit, 235 . .. IDBF processing unit, 236 . . . Range detection unit, 250 . . . Anglerange setting unit, 301 . . . Moving body, 302 . . . Electronic ScanningType Radar Device, 303 . . . Transmission wave, 304 . . . Target, 305 .. . Reflection wave, 306 . . . Computer

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, a first embodiment of an electronic scanning type radardevice (FMCW type milliwave radar) according to the present invention isdescribed with reference to the diagrams. FIG. 1 is a block diagramshowing an example of a configuration of the first embodiment.

In this diagram, the electronic scanning type radar device according tothe first embodiment includes a reception antenna 11˜1 n, a mixer (beatsignal generation unit) 61˜6 n, a transmission antenna 3, a distributor4, a filter 51˜5 n, a SW (switch) 6, an ADC (A/D converter) 7, a controlunit 8, a triangular wave generation unit 9, a VCO 10, and a signalprocessing unit 20.

The signal processing unit 20 includes a memory (memory unit) 21, afrequency resolution processing unit 22, a peak detection unit 23, apeak combination unit 24, a distance detection unit 25, a velocitydetection unit 26, a pair confirmation unit 27, a correlation matrixcomputation unit 28, a correlation matrix filtering unit 29, a directiondetection unit 30, a target confirmation unit 31, and a targetconsolidation processing unit 32.

Next, an operation of the electronic scanning type radar deviceaccording to the first embodiment is described with reference to FIG. 1.

The reception antenna 11˜1 n receives a reflection wave, i.e., areception wave, which comes from a target at which a transmission wavereflects.

Each of the mixers 61˜6 n mixes a transmission wave, transmitted by thetransmission antenna 3, and a signal obtained by an amplifier amplifyinga reception wave received by each of the reception antennas 11˜1 n.Thus, each of the mixers 61˜6 n generates a beat signal corresponding toeach difference in frequency.

The transmission antenna 3 transmits to a target, a transmission wave,which is a transmission signal obtained by the VCO (Voltage ControlledOscillator) 10 frequency-modulating a triangular wave signal generatedby the triangular wave generation unit 9.

The distributor 4 distributes a frequency-modulated transmission signalfrom the VCO 10 to the mixers 61˜6 n and to the transmission antenna 3.

Each of the filters 51˜5 n executes a band limitation on beat signalsCh1˜Chn, each of which were generated respectively by the mixers 61˜6 n,corresponding to each reception antenna 11˜1 n. In this way, each of thefilters 51˜5 n outputs the band-limited beat signal to the SW (switch)6.

The SW 6 outputs to the ADC (A/D converter) 7, a beat signal of Ch1˜Chncorresponding to each reception antennas 11˜1 n which traveled througheach of the filters 51˜5 n corresponding to a sampling signal entered bythe control unit 8, switching in succession.

The ADC 7 converts the beat signals of Ch1˜Chn, corresponding to each ofthe reception antennas 11˜1 n and entered by the SW 6 in synchrony withthe sampling signal, to a digital signal by performing an A/D conversionin synchrony with the sampling signal. The ADC 7 also stores the digitalsignal in series into a wave form memory region of the memory 21 of thesignal processing unit 20.

The control unit 8 includes a micro computer and the like. The controlunit 8 controls the overall electronic scanning type radar device shownin FIG. 1 based on a control program stored in a ROM, not diagramed, andthe like.

<Principle of Detecting the Distance, Relative Velocity, and Angle(Direction)>

Next, the principle of detecting a distance between the electronicscanning type radar device and a target, a relative velocity, and anangle (direction) is briefly described using FIGS. 2A and 2B. Thisprinciple is utilized by the signal processing unit 20 in the firstembodiment.

FIGS. 2A and 2B show a transmission signal, which was obtained by theVCO 10 frequency-modulating a signal generated by the triangular wavegeneration unit 9 shown in FIG. 1, and a condition in which thetransmission signal is reflected from the target and is entered as areception signal. The example in FIGS. 2A and 2B shows an instance inwhich there is one target.

As FIG. 2A indicates, a reception signal, which is a reflection wavefrom a target, is received, with respect to the transmitted signal, witha lag in the right direction (direction of time lag) in proportion tothe distance from the target. In addition, the reception signalfluctuates in the longitudinal direction (frequency direction) withrespect to the transmission signal in proportion to the relativevelocity with respect to the target. Furthermore, after the frequencymodulation (such as a Fourier transform, DTC, Hadamard transform, andwavelet transformation) of the beat signal obtained in FIG. 2A, thesignal has a peak value in each of the ascending region and thedescending region, as shown in FIG. 2B, when there is one target. Here,the horizontal axis of FIG. 2B represents the frequency, and thevertical axis represents the intensity.

The frequency resolution processing unit 22 performs a frequencyresolution on each of the ascending portion (ascending) and thedescending portion (descending) of the triangular wave from the sampleddata of the beat signal stored in the memory 21. For example, thefrequency resolution processing unit 22 performs a frequency modulationinto a discrete time by, for example, a Fourier transform.

As a result, in the ascending portion and the descending portion, agraph of the signal level for each beat frequency, which wasfrequency-resolved in each of the ascending portion and in thedescending portion, is obtained, as shown in FIG. 2B.

Then, the peak detection unit 23 detects the peak value from a signallevel for each beat frequency shown in FIG. 2B, and detects theexistence of a target. At the same time, the peak detection unit 23outputs the beat frequency (both the ascending portion and thedescending portion) of the peak value as a target frequency.

Next, the distance detection unit 25 computes the distance from Equation(1) shown below from the target frequency fu of the ascending portionand a target frequency fd of the descending portion inputted from thepeak combination unit 24.(Equation 1)r={C·T/(2·Δf)}·{(fu+fd)/2}  (1)

Further, the velocity detection unit 26 computes the relative velocityfrom Equation (2) shown below from the target frequency fu of theascending portion and the target frequency fd of the descending portioninputted from the peak combination unit 24.(Equation 2)v={C/(2·f0)}·{(fu−fd)/2}  (2)

In the above equations for computing the distance r and the relativevelocity v,

-   -   C: optical velocity    -   Δf: width of the frequency modulation of the triangular wave    -   f0: central frequency of the triangular wave    -   T: modulation time (ascending portion/descending portion)    -   fu: target frequency in the ascending portion    -   fd: target frequency in the descending portion

Next, the reception antenna 11˜1 n according to the first embodiment isan array-type antenna which is placed at an interval d, as shown in FIG.3.

An incoming wave from a target (incident wave, which is a reflectionwave from the target with respect to the transmission wave transmittedby the transmission antenna 3) enters the reception antenna 11˜1 n froma direction at an angle of θ degrees from the axis perpendicular to thesurface of the antenna which is lined up.

At this time, the incoming wave is received by the reception antenna11˜1 n at the same angle.

A phase difference “d_(n-1)·sin θ,” which is obtained by this same anglesuch as the angle θ and the interval d between each antenna, occursbetween each adjacent antenna.

This phase difference can be used to perform a digital beam forming(DBF), which is an additional Fourier transform, in the antennadirection, of the value which underwent a frequency resolutionprocessing for each antenna in the temporal direction. The phasedifference can also be used to detect the angle θ in a signal processingof a super resolution algorithm and the like.

<Signal Processing of a Reception Wave by the Signal Processing Unit 20>

Next, the memory 21 stores a time-series data (the ascending portion andthe descending portion), which was obtained by A/D modulating thereception signal by the ADC 7 with respect to the wave form storingregion, so that each time-series data corresponds to each antenna 11˜1n. For example, when 256 pieces are sampled in each of the ascendingportion and the descending portion, 2×256(pieces)×(number of antennas)numbers of data are stored in the wave form storing region.

The frequency resolution processing unit 22 outputs a frequency pointindicating a beat frequency, and also outputs a complex number data ofthe beat frequency. The frequency point is obtained by performing aFourier transform, for example, and modulating each beat signalcorresponding to each of Ch1˜Chn (each antenna 11˜1 n) into a frequencyat a predetermined resolution performance. For example, when each of theascending portion and the descending portion for each antenna has 256pieces of sampled data, the beat signal is modulated into a beatfrequency as a frequency region data of the complex number for eachantenna. Thus, the beat signal becomes 128 pieces of complex number data(2×128 pieces×data for the number of antennas) for each of the ascendingportion and the descending portion. In addition, the beat frequency isindicated by the frequency point.

Here, the only difference between each of the complex number data foreach antenna is the phase difference which depends on the angle θ. Theabsolute value (such as the reception intensity or the amplitude) ofeach complex number data on the complex plane is equal.

The peak combination part 24 selects the target frequency and detectsthe existence of a target for each beat frequency by detecting a beatfrequency, which has a peak value exceeding a predetermined value, froma peak of the signal intensity (or the amplitude) using a complex numberdata with respect to the peak value of each intensity for the ascendingregion and the descending region of the triangular wave of the beatfrequency which was frequency-modulated.

Therefore, the peak detection unit 23 can detect each peak value of thespectrum as a beat frequency, in other words, an existence of a targetwhich depends on the distance, by converting the complex number data foreither one of the antennas, or the added value of the complex numberdata for all of the antennas, into a frequency spectrum. By the additionof the complex number data for all of the antennas, the noise element isaveraged, and the S/N ratio increases.

The peak combination unit 24 combines the beat frequency and its peakvalue, entered by the peak detection unit 23 and shown in FIG. 4, with abeat frequency of each ascending region and the descending region andits peak value, in a matrix fashion in a round-robin matter. In otherwords, the peak combination unit 24 combines all of the beat frequenciesin each of the ascending region and the descending direction. Thus, thepeak combination unit 23 outputs, in series, to the distance detectionunit 25 and the velocity detection unit 26. Here, the horizontal axis ofFIG. 4 indicates the frequency point of the beat frequency, while thevertical axis indicates the level (intensity) of the signal.

The distance detection unit 25 computes the distance r to the targetbased on a value obtained by adding the beat frequency of thecombination for each ascending region and the descending region, whichare inputted in series.

Further, the velocity detection unit 26 computes the relative velocity vwith respect to the target by the difference in the beat frequency ofthe combination for each ascending region and the descending region,which are inputted in series.

The pair confirmation unit 27 generates a table shown in FIG. 5 from theinputted distance r, the relative velocity v, the peak value level ofdescent pu, and the peak value level of ascent pd. Moreover, the pairconfirmation unit 27 determines an appropriate combination of the peakof each ascending region and the descending region corresponding to eachtarget. The pair confirmation unit 27 thus confirms the pair of the peakof each ascending region and the descending region as a table shown inFIG. 6. The pair confirmation unit 27 then outputs the number of thetarget cluster, indicating the confirmed distance r and the relativevelocity v, to the target confirmation unit 31. FIG. 6 indicates thedistance, relative velocity, and the frequency point (the ascendingregion or the descending region) corresponding to the target clusternumber. The tables shown in FIGS. 5 and 6 are stored in the inner memoryunit of the pair confirmation unit 27. Here, the direction is notdetermined for each target cluster. Therefore, the position in thelateral direction, parallel to the direction in which the receptionantenna 11˜1 n is aligned with respect to an axis perpendicular to thedirection in which the antenna arrays of the electronic scanning typeradar device are aligned, is not determined.

Here, the pair confirmation unit 27 can, for example, select thecombination of the target clusters by prioritizing a value which isestimated in the present detection cycle from the distance r and therelative velocity v with respect to each target which was confirmed asfinal in the prior detection cycle.

In addition, the correlation matrix computation unit 28 selects the beatfrequency, which underwent a frequency resolution by the frequencyresolution processing unit 22, according to the frequency point of thebeat frequency of the target cluster for which a combination wasconfirmed by the pair confirmation unit 27. Thus, the correlation matrixcomputation unit generates a correlation matrix corresponding to thebeat frequency of either one of the ascending portion and the descendingportion (in the first embodiment, the descending portion) regarding thiscombination, and outputs to the correlation matrix filtering unit 29 andthe target consolidation processing unit 32.

Next, the target consolidation processing unit 32 links the distance r,the relative velocity v, and the frequency point f shown in FIG. 6 andinputted from the pair confirmation unit 27 with the target of the pastdetection cycle stored in the memory 21. Then, the target consolidationprocessing unit 32 outputs the past correlation matrix for each targetto the correlation matrix filter 29.

The correlation matrix filtering unit 29 multiplies each of the pastcorrelation matrix inputted from the target consolidation processingunit 32 and the present correlation matrix with a weighting coefficient.Then, the correlation matrix filtering unit 29 performs an averagingoperation on these correlation matrices. The correlation matrixfiltering unit 29 outputs the averaged correlation matrix, obtained as aresult of the averaging operation, to the direction detection unit 30.

The direction detection unit 30 uses a super-resolution algorithm suchas MUSIC to detect the direction of the corresponding target from theaveraged correlation matrix, and outputs to the target confirmation unit31.

In addition, the target consolidation processing unit 32 adds to thepresent correlation matrix, the identifying information regarding thedistance, the relative velocity, and the direction outputted from thetarget confirmation unit 31, and stores into the memory 21.

<Super-Resolution Algorithm in the Estimation of the Arrival Directionof an Incoming Wave>

Next, a super-resolution algorithm estimating the arrival direction ofan incoming wave according to the correlation matrix computation unit28, the correlation matrix filtering unit 29, and the directiondetection unit 30, is described with MUSIC as an example with referenceto FIG. 7. FIG. 7 is a flowchart describing the flow of the operatingprocess of a general MUSIC Method. Since the process of the MUSIC Methoditself is used in general (for example, in Non-Patent Documents 1 and 2,or, Patent Documents 3-6), only the aspects of the MUSIC Method whichare necessary in the first embodiment are described.

The frequency resolution processing unit 22 reads in the beat signal ofthe reception wave stored in the memory 21 (step S101), and performs afrequency-modulation on the beat signal for each antenna (step S102).

Further, as described above, the correlation matrix computation unit 28reads in the complex number frequency region data (hereinafter referredto as complex number data) by making a selection from the frequencyresolution processing unit 22. The complex number data has undergone afrequency resolution, and corresponds to the frequency point of thetarget in the descending region for which a pair has been confirmed bythe pair confirmation unit 27. In addition, regarding the descendingregion, the correlation matrix computation unit 28 generates acorrelation matrix indicating the correlation for each antenna (stepS103).

The generation of the correlation matrix by the correlation matrixcomputation unit 28 in step S103 is conducted, for example, according tothe methods shown in FIGS. 8A and 8B. The methods shown in FIGS. 8A and8B are briefly described below.

According to the method shown in FIG. 8A, the correlation matrixcomputation unit 28 generates a correlation matrix (complex correlationmatrix) based on the bare complex number data (step S103_1), andprocesses with a forward-only spatial average (Forward Spatial AveragingMethod) or a forward-and-backward spatial average (Forward-BackwardSpatial Averaging Method) (step S103_2).

Spatial averaging refers to a process in which the number of antennas inthe array of the original reception antennas is divided into subarrayswhich has a lesser amount of antennas, and the subarrays are averaged.The phase relation of waves having a correlation differs according tothe position at which the wave was received. Thus, according to thisbasic principle of spatial averaging, the correlation matrix is obtainedby moving the reception point in an appropriate manner. In this way, thebasic principle of spatial averaging is such that the correlation of thecorrelated interference wave is restrained due to the effect of theaveraging process. In general, the averaging is conducted by taking outa plurality of subarrays having the same alignment from the overallarray of reception antennas without moving the array of receptionantennas, and then obtaining the average of each correlation matrix.

For example, as shown in FIG. 9, when the array of reception antennas11˜1 n is such that there are nine antennas (n=9), the correlationmatrix computation unit 28 obtains the backward correlation matrixCR^(b) _(f) in the latter equation (6) with respect to the correlationmatrix CR^(f) _(f) in the forward equation (5) indicated below. Thus,the correlation matrix computation unit 28 carries out an averagingprocedure of the forward/backward elements by averaging thecorresponding elements in the correlation matrix in equation (5) and thebackward correlation matrix in equation (6) according to the followingequation (3).(Equation 3)CR ^(fb) _(f)=(CR ^(f) _(f) +CR ^(b) _(f))/2  (3)

In this way, the correlation matrix computation unit 28 divides thecorrelation matrix CR^(fb) _(f), obtained by the forward/backwardaveraging process, into subarrays, and computes an average. Thus, thecorrelation matrix computation unit 28 obtains a correlation matrix Rxxwhich is used to estimate the arrival direction of the reception wave.In other words, the correlation matrix obtained by the forward/backwardspatial averaging process can be expressed as follows by Equation (4).(Equation 4)Rxx=(CR ^(fb1) _(f) +CR ^(fb2) _(f) +CR ^(fb3) _(f))/3  (4)

Here, the correlation matrix computation unit 28 obtains the correlationmatrix Rxx by dividing the nine reception antennas 11˜19 into threesubarrays each of which including seven antennas 11˜17, 12˜18, and13˜19, and by averaging the corresponding elements of each matrix in thesubarray.

$\begin{matrix}\left( {{Equation}\mspace{14mu} 5} \right) & \; \\{{CR}_{f}^{f} = \begin{bmatrix}W_{11} & W_{12} & W_{13} & W_{14} & W_{15} & W_{16} & W_{17} & W_{18} & W_{19} \\W_{21} & W_{22} & W_{23} & W_{24} & W_{25} & W_{26} & W_{27} & W_{28} & W_{29} \\W_{31} & W_{32} & W_{33} & W_{34} & W_{35} & W_{36} & W_{37} & W_{38} & W_{39} \\W_{41} & W_{42} & W_{43} & W_{44} & W_{45} & W_{46} & W_{47} & W_{48} & W_{49} \\W_{51} & W_{52} & W_{53} & W_{54} & W_{55} & W_{56} & W_{57} & W_{58} & W_{59} \\W_{61} & W_{62} & W_{63} & W_{64} & W_{65} & W_{66} & W_{67} & W_{68} & W_{69} \\W_{71} & W_{72} & W_{73} & W_{74} & W_{75} & W_{76} & W_{77} & W_{78} & W_{79} \\W_{81} & W_{82} & W_{83} & W_{84} & W_{85} & W_{86} & W_{87} & W_{88} & W_{89} \\W_{91} & W_{92} & W_{93} & W_{94} & W_{95} & W_{96} & W_{97} & W_{98} & W_{99}\end{bmatrix}} & (5) \\\left( {{Equation}\mspace{14mu} 6} \right) & \; \\{{CR}_{f}^{b} = \begin{bmatrix}W_{99} & W_{89} & W_{79} & W_{69} & W_{59} & W_{49} & W_{39} & W_{29} & W_{19} \\W_{98} & W_{88} & W_{78} & W_{68} & W_{58} & W_{48} & W_{38} & W_{28} & W_{18} \\W_{97} & W_{87} & W_{77} & W_{67} & W_{57} & W_{47} & W_{37} & W_{27} & W_{17} \\W_{96} & W_{86} & W_{76} & W_{66} & W_{56} & W_{46} & W_{36} & W_{26} & W_{16} \\W_{95} & W_{85} & W_{75} & W_{65} & W_{55} & W_{45} & W_{35} & W_{25} & W_{15} \\W_{94} & W_{84} & W_{74} & W_{64} & W_{54} & W_{44} & W_{34} & W_{24} & W_{14} \\W_{93} & W_{83} & W_{73} & W_{63} & W_{53} & W_{43} & W_{33} & W_{23} & W_{13} \\W_{92} & W_{82} & W_{72} & W_{62} & W_{52} & W_{43} & W_{32} & W_{22} & W_{12} \\W_{91} & W_{81} & W_{71} & W_{61} & W_{51} & W_{41} & W_{31} & W_{21} & W_{11}\end{bmatrix}} & (6)\end{matrix}$

Meanwhile, in the case of the forward spatial averaging, the matricesfrom V₁₁ to V₉₉ can be kept as the matrices from W₁₁ to W₉₉ in equation(5). Thus, it is not necessary to average each element as shown, forexample, in equation (7).(Equation 7)V ₁₁=(W ₁₁ +W ₉₉)/2  (7)

Regarding the use in which the arrival direction of the reception waveregarding the radar is estimated, all of the incoming reception wavesare reflection waves caused by the transmitted transmission wavereflecting from the target. Therefore, the data of the reception wavesreceived by each antenna exhibits a strong correlation with one another.Thus, the results of the eigen value computation in the latter phase arenot obtained accurately. In this way, spatial averaging has an effect ofrestraining the correlation, extracting a self correlation, andaccurately estimating the direction of the incoming wave.

Next, the correlation matrix computation unit 28 performs a unitaryconversion in order to convert the correlation matrix of complex data,which underwent a spatial averaging process as described above, into acorrelation matrix of real numbers.

Here, by converting into a correlation matrix of real numbers, the eigenvalue computation in a subsequent step which has the heaviestcomputation load can be executed using real numbers only. In this way,the computation load can be greatly reduced.

Meanwhile, FIG. 8B shows a variation in which the eigen valuecomputation in the subsequent step is executed using complex numberswithout converting into a correlation matrix of real numbers byperforming a unitary conversion as indicated in FIG. 8A.

Further, in step S103, regarding the correlation matrix Rxx obtained bythe step S103_3 in FIG. 8A and the step S103_2 in FIG. 8B, the values ofeach element can be normalized (i.e., divided by the maximum value)based on the maximum value of the correlation matrix (or the diagonalelement of the correlation matrix).

Next, the direction detection unit 30 computes the eigen value of thecorrelation matrix Rxx obtained in step S103 (in actuality, thecorrelation matrix obtained after the correlation matrix filteringprocess described below) and its corresponding eigen vector as an eigenvalue λ and an eigen vector e which satisfies the followingcharacteristic equation (step S104).(Equation 8)Rxxe=λe  (8)

Then, based on the eigen value λ obtained above, the direction detectingunit 30 estimates the number of incoming waves necessary to remove thesignal component vector (step S105).

Next, the direction detection unit 30 generates a spectrum of angles bycomputing an inner product of a vector with only the noise componentsafter removing the signal vector, and a vector for each direction andangle which is predetermined internally (step S106). As a result, it ispossible to associate a null with a directional characteristic to thearrival direction of the incoming wave.

Further, the direction detection unit 30 detects a peak from thespectrum of angles which exceeds a predetermined threshold value. Inthis way, the direction detection unit 30 detects the peak and computesthe direction of the incoming wave (angle θ) (step S107).

In addition, the direction detection unit 30 can make a conversion to aposition in the lateral direction with respect to the vertical axis ofthe array of antennas of the electronic scanning type radar device basedon the angle (i.e., the arrival direction of the reception wave) and thedistance computed by the distance detection unit 25.

A standard MUSIC Method has been described above. In the MUSIC spectrumcomputation in step S106, it is possible to use a method called theRoot-MUSIC Method which computes a solution from the root of thepolynomial, instead of a type searching with a direction vector.

In addition, after the step S107 in FIG. 7, it is possible to add aprocess computing the received electronic power and deleting anunnecessary wave (data of an unnecessary reception wave).

In other words, the direction detection unit 30 compares the electronicpower indicated in the diagonal component of the matrix S in thefollowing equation with a predetermined threshold value, and detectswhether or not the electronic power exceeds the threshold value.Further, the direction detection unit 30 has a process which makes adetermination of necessary reception wave when the electronic powerexceeds the threshold value, and, meanwhile, makes a determination ofunnecessary reception wave when the electronic power is less than orequal to the threshold value.(Equation 9)S=(A ^(H) A)⁻¹ A ^(H)(Rxx−σ ² I)A(A ^(H) A)⁻¹  (9)

Here, S indicates the correlation matrix of the signal of the receptionwave, A indicates the directional matrix, A^(H) indicates the conjugatetranspose matrix of A, I indicates the unit matrix, Rxx indicates thecorrelation matrix computed by the correlation matrix computation unit28, and σ² indicates the dispersion of the noise vector.

By adding the process, described above, of computing the receivedelectronic power and deleting an unnecessary wave, it is possible todelete the unnecessary incoming reception wave, when the number ofreception waves was overestimated in the estimation of the number ofreception waves in step S105.

<The Present and Past Averaging Process by the Correlation MatrixFiltering Unit 29>

Next, following is a description of the averaging process of the presentand past correlation matrices according to the first embodiment. Thisaveraging process is conducted primarily by the correlation matrixcalculation unit 28, the correlation matrix filtering unit 29, and thetarget consolidation processing unit 32 in FIG. 1.

In order to perform the averaging process in the correlation matrixfiltering unit 29, the target consolidation processing unit 32 conductsthe following operation so that, in the table shown in FIG. 10, aconsolidation is made for each target among the present target cluster(t), a target (t) predicted from the confirmed past target data, and atarget confirmed in the past (t-1, t-2, t-3).

The t-1 shown in FIG. 10 indicates a result of the detected cycle whichis one cycle prior (immediately prior) to the present. The t-2 indicatesa result of the detected cycle which is two cycles prior to the present.The t-3 indicates a result which is three cycles prior to the present.

As a result of each detection cycle, respectively for each confirmedtarget, the distance r, the longitudinal position Long_d (a verticaldirection with respect to the direction in which the antenna isaligned), the lateral position Late_d (a position parallel to thedirection in which the antenna is aligned), the relative velocity withrespect to the target veto (i.e., v), a descending peak frequency pointf_dwn, and the correlation matrix mat_dwn at the time of the descendingpeak frequency (i.e., Rxx), are stored in the memory 21 in the form ofthe table shown in FIG. 10 (A case, for example, in which the descendingdata is used for detecting the direction. In addition, more accurately,the memory region of mat_dwn is larger than others. However, the memoryregion of mat_dwn is presumed to be the same for convenience, for easeof displaying on the table). Here, the longitudinal position Long_d ofthe target and the lateral position Late_d can be obtained from theangle with the target (the angle of the arriving direction of thereception wave) and the distance r. When the angle is θ and the distanceis r, the longitudinal position Long_d is computed by r·cos θ, and thelateral position is computed by Long_d·sin θ.

In addition, the target consolidation processing unit 32 predicts adistance r of each target at the time of the present cycle, thelongitudinal position Long_d and the lateral position Late_d, therelative velocity, and the peak frequency point based on the targetdistance r which was confirmed in the past, the longitudinal positionLong_d, the lateral position Late_d, and the relative velocity velo. Forexample, in order to predict the longitudinal position Long_d, thelateral position Late_d, and the frequency point, a movable range duringthe time after the detected cycle is determined based on the previousdistance r, the longitudinal position Long_d, the lateral positionLate_d, and the relative velocity. The relative velocity can bepredicted by computing, for example, the slope of the change in thetransition of the value of the relative velocity for several cycles inthe past.

For instance, the target consolidation processing unit 32 sets apredetermined movable range, a frequency point range, and a relativevelocity range corresponding to each of the distance r predicted fromthe results confirmed in the past, the longitudinal position Long_d, thelateral position Late_d, the peak frequency point, and the relativevelocity. In addition, the target consolidation processing unit 32determined whether or not each value, computed in the present cycle, iswithin the range. If the value computed in the present cycle is outsidethe range, the target consolidation processing unit 32 determines thatthe target is a different one.

Further, in the table shown in FIG. 10, if the target in the presentdetection cycle is consolidated with a past target, the targetconsolidation processing unit 32 moves the result of t-2 to t-3, movesthe result of t-1 to t-2, and moves the result of the present detectioncycle to the result of t-1. In this way, the target consolidationprocessing unit 32 computes the result of the estimation in the nextcycle.

Meanwhile, the target consolidation processing unit 32 regards thepresent target, which is not linked with any of the results of thetarget in the past, as a new target. In order to estimate the directionwithout conducting a filtering with the past correlation matrix, thecorrelation matrix Rxx is directly outputted to the direction detectionunit 30.

When there is a past target that cannot be linked to the result of thepresent target cluster, the target consolidation processing unit 32clears all of the information of such a past target.

Therefore, when a target enters a distance under the influence of amultipass, and when the detection cycle is such that a peak detection ofthe beam frequency is not made, the filtering effect using the result ofthe past target cluster is reset. In the case of the first embodimentshown in FIG. 10, the results of the target in three past detectioncycles are stored in the memory 21.

Moreover, in another embodiment, the target consolidation processingunit 32 may be configured so that, even if a past target is detectedwhich was not linked to the target in the present detection cycle, theconfirmed result of the past target is maintained for a predeterminednumber of cycles.

In addition, the target consolidation unit 32 may be configured so thatthe prediction result, estimated based on a past result, is updated inseries. Further, the target consolidation unit 32 may be configured sothat, even if a target in the present detection cycle is not detecteddue to the influence of a multipass, and when a linkage is madesubsequent to the next detection cycle, the past data, other than thenumber of cycles for which the peak cannot be detected due to theinfluence of the multipass, can be used in the filtering process.

In addition, similar to the extrapolation method in tracking, theprediction result may be used as a result of the present detection cyclein a detection cycle in which the peak value is not detected. In thisway, the existence of the target can be maintained.

Further, as shown in FIG. 11, the correlation matrix filtering unit 29performs an averaging operation of the correlation matrix Rxx regardingthe process in the step S103_3 in FIG. 8A. Thus, a correlation matrixfor estimating the arrival direction of the reception wave is generated.

Here, after the computation of the present correlation matrix of realnumbers computed from the complex number data of the present detectioncycle (unitary conversion, step S103_3_1), the correlation matrixfiltering unit 29 performs a weighted averaging process with acorrelation matrix for one past detection cycle or more in the tableshown in FIG. 10 and stored in the memory 21 (step S103_3_2).

Incidentally, the same value can be ultimately obtained by storing thecondition of the complex number correlation matrix of the step S103_1 ofFIG. 8A in the memory 21, and performing the averaging process,described above, before the spatial averaging process in step S103_2 andbefore the unitary conversion in step S103_3. However, since the amountof data stored in the memory 21 increases, it is preferred to use amethod in which a correlation matrix of real numbers, obtained byunitary conversion, is stored.

For instance, FIG. 12 shows an example in which a 5-by-5 correlationmatrix (real numbers) is created by performing a subarraying operationin the spatial averaging process.

In this example, the result of the past detection cycle stored in thememory 21 is a result up to three cycles prior to the present, and canbe expressed by the following equation (10).(Equation 10)Rxx′(t′)=K1·Rxx(t)+K2·Rxx(t−1)+K3·Rxx(t−2)+K4·Rxx(t−3)  (10)

Further, when the weighting coefficient in the above equation (10) issuch that K1 (Present)=K2 (one cycle prior to the present)=K3 (twocycles prior to the present)=K4 (three cycles prior to thepresent)=0.25, a simple average of the four correlation matrices isobtained.

In addition, it is possible to change the magnitude of the weightingcoefficient for each cycle. For example, it is possible to increase theweighting coefficient closer to the present cycle, or multiply a cyclenot included in the average with a coefficient zero. There is notparticular limit on the number of past cycles. However, considering thefiltering effect and the memory capacity, it is presumed that up tothree past cycles prior to the present in the first embodiment isappropriate.

The correlation matrix filtering unit 29 outputs the correlation matrixRxx′, described above, to the direction detection unit 30 as acorrelation matrix used to estimate the arrival direction of thereception wave.

Meanwhile, when the averaging process is performed using the complexcorrelation matrix shown in FIG. 8B, the processing step shown in FIG.13 is executed in the step S103_1.

The correlation matrix filtering unit 29 computes the present complexcorrelation matrix (step S103_1_1) calculated by the complex number dataof the present detection cycle. Then, the correlation matrix filteringunit 29 performs a weighted-averaging process (step S103_1_2) with acomplex number correlation matrix for one or more past cycles stored inthe memory 21. In FIG. 13, as another embodiment different from theexample in FIG. 11, a correlation matrix filtering process was conductedon the complex number correlation matrix which has not yet beenspatially averaged. However, in this case as well, the amount ofcomputation and the amount of data stored in the memory can be keptsmall if a correlation matrix filtering process is performed on thecomplex number correlation matrix after being spatially-averaged, asshown in step S103_2 in FIG. 8B. Here, when the relative velocity withrespect to the target is extremely large, the change in the distance foreach detection cycle of the target becomes large.

Therefore, the range of the beat frequency filtered by the correlationmatrix filtering unit 29 (i.e., the distance range) may widen, and thechange in the angle θ may increase between the cycles of linked targets.

In response to such cases, when the correlation matrices of a sametarget in the past detection cycle is linked as shown in FIGS. 14A and14B, the past detection cycle of the stored correlation matrix can bekept intact by setting the beat frequency point range which can belinked from the result of the present detection cycle, and thus it ispossible to select the number of past cycles that will be used when theaveraging process is performed. It is also possible to reduce thesubstantive number of linkage by varying the weighing coefficient.

Incidentally, FIG. 14B shows an example where the target is approachingwith a fast relative velocity. In this case, the peak of the beatfrequency moves quickly. As a result, the cycle t-3 falls outside therange of data that will be averaged. Therefore, the number of pastdetection cycles of the correlation matrix stored as the table in FIG.10 may be kept intact, the number of past cycles used at the time ofaveraging may be selected, or the number of linkage can be reducedsubstantively by varying the weighting coefficient (for example,changing the weighing coefficient of the correlation matrix to “0”).

In addition, a threshold value may be set for the relative velocityregarding the result concerning the target in the past detection cycleand regarding the result concerning the target in the present detectioncycle.

In this case, when either of the relative velocity regarding the resultconcerning the target in the past detection cycle and regarding theresult concerning the target in the present detection cycle is greaterthan or equal to a relative velocity of the predetermined thresholdvalue, the correlation matrix filtering unit 29 may be configured sothat the number of past cycles that are averaged is reduced, or thenumber of linkage is reduced substantively by varying the weighingcoefficient.

In addition, according to yet another configuration of the correlationmatrix filtering unit 29, the change in the value of the lateralposition which is confirmed in the target in the past detection cyclemay be directly calculated, then, whether or not the predeterminedprescriptive value was exceeded may be calculated, and if thepredetermined prescriptive value is exceeded, the number of cycles thatare averaged may be reduced, or, the weighting coefficient may be variedsuch that the number of elements in the series may be substantivelyreduced. For example, in each of the present cycle and the past cycle, athreshold value ΔLate_d may be set, and, for example, when a lateralmovement of greater than or equal to ΔLate_d is detected between t-1 andt-2, the weighting coefficient of the data of t-2 and t-3 may be set tobe 0. After a direction is detected by the direction detection unit 30,the target confirmation unit 31 stores the distance of the target, thelongitudinal position, the lateral position, the relative velocity, thedescending peak frequency point, and the correlation matrix, withrespect to the table shown in FIG. 10 of the memory 21 via the targetconsolidation processing unit 32, as described above, as information oft-1 for the next detection cycle, and deletes information of t-3.

In addition, the signal processing unit 40 shown in FIG. 15 is aconfiguration corresponding to the signal processing unit 20 shown inFIG. 1. In the result of each target cluster shown in the table in FIG.10 in the memory 21, the configuration may be such that the complexnumber data after the frequency resolution is stored instead of thecorrelation matrix. The same reference numeral is used for theconfiguration performing a similar process. Only the aspects which aredifferent from the configuration in FIG. 1 are described.

The frequency dissolution processing unit 42 outputs the frequency datato the target consolidation processing unit 52, which is a complexnumber data after the frequency dissolution. The remaining process ofthe frequency dissolution processing unit 22 is similar to what is shownin FIG. 1.

In addition, regarding the distance, longitudinal position, lateralposition, relative velocity, the descending peak frequency pointconfirmed by the target confirmation unit 31, and the correlationmatrix, the target consolidation processing unit 52 converts the complexnumber data corresponding to this correlation matrix into a correlationmatrix, and stores it into table 10. The remaining process of the targetconsolidation processing unit 52 is similar to the target consolidationprocessing unit 32 shown in FIG. 1.

According to the configuration shown in FIG. 15 described above, thedata stored in the memory 21 becomes less compared to the correlationmatrix. However, in the correlation matrix filtering unit 29, when thepresent correlation matrix and the past correlation matrix are averaged,the it is necessary that the correlation matrix filtering unit 29recalculate the correlation matrix Rxx from the complex number data ofthe result of the past detection cycle. FIG. 16 shows the processingflow corresponding to FIG. 11. FIG. 17 shows the processing flowcorresponding to FIG. 13. In this case in FIG. 16, as in the example inFIG. 17, the averaging process by the correlation matrix filter wasconducted before the spatial averaging operation and the unitaryconversion, which is preferable because the amount of computation issmall.

Second Embodiment

Hereinafter, an electronic scanning type radar device according to asecond embodiment of the present invention is described with referenceto FIG. 18. FIG. 18 is a block diagram showing an example of aconfiguration of the electronic scanning type radar device according tothe second embodiment.

Similar to the first embodiment, the second embodiment is configured sothat the direction is estimated only with a super-resolution algorithm.The same reference numeral is used for the configuration which issimilar to the first embodiment shown in FIG. 1. Hereinafter, theaspects which are different from the first embodiment are described.

The frequency dissolution processing unit 22B converts the beat signalof the ascending region and the descending region for each antenna intocomplex number data, and outputs the frequency point indicating its beatfrequency and the complex number data to the peak detection unit 23B.

Then, the peak detection unit 23B detects the peak value of each of theascending region and the descending region, and the frequency point forwhich the peak value exists, and outputs the frequency point to thefrequency dissolution processing unit 22B.

Next, the frequency dissolution processing unit 22B outputs the complexnumber data corresponding to each of the ascending region and thedescending region to the next correlation matrix computation unit 28.

The correlation matrix computation unit 28 generates a correlationmatrix from the inputted complex number data.

This complex number data becomes the target cluster of the ascendingregion and the descending region (the beat frequency which has a peak inthe ascending region and the descending region).

Since it is necessary that target confirmed in the past and bothascending and descending target clusters be consolidated by the targetconsolidation processing unit 32B, the table shown in FIG. 19 is storedin the memory 21. The table shown in FIG. 19 stores, in addition to theconfiguration of FIG. 10, the frequency point (peak frequency) in theascending region (ascent) and the descending region (descent) for eachtarget cluster, and the correlation matrix corresponding to thefrequency point of the ascending region and the descending region.

The target consolidation unit 32B performs a consolidation operation ofthe present detection cycle and the past detection cycle based on aprocess similar to the target consolidation 32 in FIG. 1.

Further, in each of the ascending region and the descending region, thecorrelation matrix filtering unit 29 performs an averaging operation onthe correlation matrix in the present detection cycle and thecorrelation matrix in the past detection cycle, and outputs to thedirection detection unit 29.

Next, the direction detection unit 30 detects an angle θ for each of thecorrelation matrix of the ascending region and the correlation matrix ofthe descending region, and outputs to the peak combination unit 24B as atable shown in FIG. 20.

Further, based on the information of the table shown in FIG. 20, thepeak combination unit 24B creates a combination having similar angles,and outputs a combination of the beat frequency of the ascending regionand the descending region to the distance detection unit 25 and thevelocity detection unit 26.

Similar to the first embodiment, the distance detection unit 25 computesa distance based on the beat frequency of the ascending region and thedescending region of the combination.

In addition, similar to the first embodiment, the velocity detectionunit 26 computes the relative velocity based on the beat frequency ofthe ascending region and the descending region of the combination.

Here, regarding the values of the distance and the relative velocity, itis not necessary to perform an averaging process and a filtering processon the present detection cycle and the past detection cycle as in thedirection detection, each of the distance detection unit 25 and thevelocity detection unit 26 performs a calculation based on a combinationof the ascending region and the descending region of the beat frequencyof the present detection cycle.

The target confirmation unit 31B confirms the above describedcorrelation matrix of the ascending region and the descending region,the frequency point, the distance, and the relative velocity in theascending region and the descending region as the present condition.

In addition, the target consolidation processing unit 32B stores, foreach target, the frequency point of the ascending region and thedescending region, the correlation matrix, the distance, thelongitudinal position, the lateral position, and the relative velocityof the ascending region and the descending region, which are inputtedfrom the target confirmation unit 31B, into a table in FIG. 19 by asimilar process conducted in the first embodiment.

In addition, in the second embodiment, a configuration may be made suchthat a complex number data of the beat frequency for which a peak valuewas detected is stored in the table in FIG. 19, instead of thecorrelation matrix. Here, in the second embodiment, not only the complexnumber data corresponding to the descending region in the firstembodiment, but also the complex number data of both the ascendingregion and the descending region are stored in the table of FIG. 19 witha correspondence to the frequency point of each beat frequency.

According to this configuration of storing the complex number data, whenthe correlation matrix filtering unit performs, for each target cluster,an averaging operation of the correlation matrix of the presentdetection cycle and the correlation matrix of the past detection cycle,the correlation matrix computation unit 28 the correlation matrixcomputation unit 28 computes a correlation matrix based on the complexnumber data of the past detection cycle read from the memory 21.

Third Embodiment

Hereinafter, an electronic scanning type radar device according to athird embodiment of the present invention is described with reference toFIG. 21. FIG. 21 is a block diagram showing an example of aconfiguration of the electronic scanning type radar device according tothe third embodiment.

According to this third embodiment, different from the first embodiment,an estimation of a direction is first made using a DBF (Digital BeamForming) which has a lower resolution performance compared to asuper-resolution algorithm such as the MUSIC Method. Next, asuper-resolution algorithm is used to estimate the direction from acorrelation matrix which has undergone an averaging process. The samereference numeral is used for the configuration which is similar to thefirst embodiment shown in FIG. 1. Hereinafter, the aspects which aredifferent from the first embodiment are described.

As shown in FIG. 21, a DBF processing unit 40 is provided between thefrequency dissolution processing unit 22 in the first embodiment shownin FIG. 1 and the peak detection unit 23. As described above, the thirdembodiment differs from the first embodiment in that an arrivaldirection of the reception wave is first estimated using DBF.

Similar to the first embodiment, the frequency dissolution processingunit 22 performs a frequency resolution on the inputted beat signal(temporal axis Fourier transform), and outputs a frequency pointindicating the beat frequency and the complex number data to the DBFprocessing unit 40.

Next, the DBF processing unit 40 performs a Fourier transform on theinputted complex number data corresponding to each antenna in thedirection in which the antenna is aligned. In other words, the DBFprocessing unit 40 performs a spatial axis Fourier transform.

Then, the DBF processing unit 40 computes the spatial complex numberdata for each angular channel corresponding to the angular resolution,which, said differently, depends on the angle, and outputs to the peakdetection unit 23 for each beat frequency.

Therefore, the spectrum, indicated by the spatial complex number data(with a unit of beat frequency) for each angular channel outputted fromthe DBF processing unit 40, depends on the estimation of the arrivaldirection of the reception wave by the beam scanning resolution.

In addition, since a Fourier transform is conducted in the direction inwhich the antenna is aligned, the same effect can be obtained as whenthe complex number data is added between the angular channels.Furthermore, the S/N ratio of the complex number data for each angularchannel is improved. Thus, the accuracy with which the peak value isdetected can be enhanced in a manner similar to the first embodiment.

As in the first embodiment, the above described complex number data andthe spatial complex number data are computed in both the ascendingregion and the descending region of the triangular wave.

Next, after the processing by the DBF processing unit 40, the peakdetection unit 23 performs a peak detection for each angular channelbased on the DBF results, and outputs the detected peak value for eachchannel to the next peak combination unit 24 for each angular channel(in the case of a spatial axis Fourier transform with a 16-resolution,15 angular channels).

Similar to the first embodiment, the peak combination unit 24 combines abeat frequency in the ascending region and the descending region whichhas a peak value, with this peak value, and outputs to the distancedetection unit 25 and the velocity detection unit 26 for each angularchannel.

Then, the pair confirmation unit 27 generates a table shown in FIG. 5for each angular channel based on the distance r and the relativevelocity v which are inputted in series from each of the distancedetection unit 25 and the velocity detection unit 26. Furthermore,similar to the first embodiment, the pair confirmation unit 27determines an appropriate combination of the peak for each of theascending region and the descending region corresponding to each targetfor each angular channel. Here, according to the resolution of the DBF,the existence of the target is indicated over multiple angular channels.Therefore, it is possible to make an appropriate combination of the peakof each of the ascending region and the descending region for eachangular channel while also considering the consistency with the adjacentangular channels (matrices). Then, the pair confirmation unit 27confirms a pair of the peak of each of the ascending region and thedescending region, outputs a target cluster number indicating theconfirmed distance r and the relative velocity v to the targetconfirmation unit 31, and creates a table shown in FIG. 22.

In addition, the pair confirmation unit 27 can obtain not only thedistance r and the relative velocity v, but also the longitudinalposition and the lateral position by getting information of the angularchannel of each target. Therefore, the pair confirmation unit 27 cancreate a table shown in FIG. 22 which has a result corresponding to eachtarget cluster of the present detection cycle including a longitudinalposition and a lateral position with respect to the table shown in FIG.6.

In addition, the target consolidation unit 32 performs a process linkingthe target in the present detection cycle with the target in the pastdetection cycle shown in FIG. 10, using the information in the tableshown in FIG. 22. Here, the target consolidation unit 32 uses thelongitudinal position and the lateral position, as a parameter for theconsolidation, in addition to the distance, the relative velocity, andthe peak frequency point. Therefore, the consolidation process can beperformed with a greater accuracy.

Furthermore, by performing an estimation based on the AND Theoryaccording to the information on the direction obtained from thedirection detection unit 30 and the information on the directionobtained from the DBF, it is possible to enhance the reliability of thedetection of the direction. In addition, it is possible to assign theinformation on the direction of one another by, for example, using theinformation on the angle of the DBF in a close distance, even if theangular resolution is rough.

Further, in the third embodiment, a configuration may be made in whichthe complex number data of the beat frequency for which a peak value hasbeen detected is stored with respect to the table shown in FIG. 10,instead of the correlation matrix.

According to this configuration in which the complex number data isstored, when the correlation matrix filtering unit 25 performs anaveraging process on the correlation matrix of the present detectioncycle and the correlation matrix of the past detection cycle for eachtarget cluster, similar to the first embodiment, the correlation matrixcomputation unit 24 computes a correlation matrix from the complexnumber data of the past detection cycle read from the memory 21.

Fourth Embodiment

Hereinafter, an electronic scanning type radar device according to afourth embodiment of the present invention is described with referenceto FIG. 23. FIG. 23 is a block diagram showing an example of aconfiguration of the electronic scanning type radar device according tothe fourth embodiment.

According to this fourth embodiment, different from the firstembodiment, an estimation of a direction is first made using a DBF(Digital Beam Forming) which has a lower resolution performance comparedto a super-resolution algorithm such as the MUSIC Method. In this way,the angular range of the target is narrowed, an IDBF (inverse DBF, inother words, an inverse spatial axis Fourier transform) is performed,thus reconverting to the complex number data of a temporal axis.Therefore, the fourth embodiment is configured so that the accuracy ofthe estimation of the direction conducted in the subsequentsuper-resolution algorithm is enhanced. The same reference numeral isused for the configuration which is similar to the third embodimentshown in FIG. 21. Hereinafter, the aspects which are different from thethird embodiment are described.

The fourth embodiment is configured so that a Ch (Channel) deleting unit41 and an IDBF processing unit 42 are added to the third embodiment.

The DBF processing unit 40 performs, similar to the third embodiment, aspatial axis Fourier transform, and outputs the spatial complex numberdata to the peak detection unit 23, and outputs to the Ch deleting unit41 as well.

Here, in the fourth embodiment in the direction in which the receptionantennas are aligned, as shown in FIG. 24A, the DBF processing unit 40performs a spatial axis Fourier transform based on a 16-pointresolution, for instance, and, as a result, creates a spectrum with anangle unit of 15 angular channels, and outputs to the Ch deleting unit41.

Then, the Ch deleting unit 41 detects whether or not the level of thespectrum of the spatial complex number data corresponding to the peakfrequency point (for example, the descending portion) of the DBF targetwhich was confirmed by the pair confirmation unit 27 is continuous whilebeing adjacent to the predetermined angular range, and, whether or notthe level of the predetermined DBF threshold value is exceeded.Furthermore, the Ch deleting unit 41 performs a process converting thespectrum of the angular channel which does not exceed the DBF thresholdvalue to “0,” and thus outputs a narrowed spatial complex number data.

According to the process described above, when, for example, fouradjacent angular channels as shown in FIG. 24B have a level exceedingthe DBF threshold value, the Ch deleting unit 41 determines that one ormore targets exist(s) in the range, and leaves the spectrum of theseangular channels intact, while converting the intensity of a spectrum ofanother angle to “0.”

Further, the IDBF processing unit 42 performs an inverse spatial axisFourier transform on a spatial complex number data such that thespectrum was narrowed, i.e., only the data of the angular channel regionbeing continuous for the predetermined number of angular channels andexceeding the DBF threshold value is left, and the intensity of the restof the region is converted to “0.” Thus, the IDBF processing unit 42restores the spatial complex number data to a complex number data of atemporal axis, and outputs to the correlation matrix computation unit28.

Furthermore, in order to compute a correlation matrix from the inputtedcomplex number data, the correlation matrix computation unit 28 canobtain a correlation matrix with a good orthogonal characteristic suchthat objects on the roadside and the like are removed and the noiseelement is deleted. FIG. 24C shows an example in which a correlationmatrix is created by the above described method with respect to thetarget cluster of the DBF resolution in FIG. 24B (the term “targetcluster” is used because, in actuality, two or more targets may exist),and the target is divided even further by a super-resolution algorithm.

In addition, as shown in FIG. 25A, when a reception wave including areflection component from a plurality of target clusters is received,there are a plurality of angular channel ranges, which exceed the DBFlevel at continuous angular channels, in the spatial complex number dataoutputted from the DBF processing unit 40.

Furthermore, regarding the inputted spatial complex number data, withinthe predetermined angular channel range, when the level of the spectrumof the adjacent angular channels continuously exceeds the level of theDBF threshold value, the Ch deleting unit 41 extracts each of theexceeded angular channel region, and converts the intensity of thespectrum outside this angular channel region to “0.” Thus, as shown inFIGS. 25B and 25C, the Ch deleting unit 41 makes a division intoseparate spatial complex number data which is recognized in the angularchannel region.

Here, as in the third embodiment, the pair confirmation unit 27 obtainsthe distance, the relative velocity, the longitudinal position, and thelateral position, outputs to the Ch deleting unit 41, and outputs to thetarget consolidation processing unit 32.

The Ch deleting unit 41 selects the spatial complex number datacorresponding to the frequency point of the DBF target, and, afterperforming the above described Ch deletion, outputs to the IDBFprocessing unit 42.

In addition, the IDBF processing unit 42 performs an inverse spatialFourier transform on the inputted spatial complex number data, andoutputs the obtained temporal axis complex number data to thecorrelation matrix computation unit 28.

As a result, the correlation matrix computation unit 28 calculates thecorrelation matrix from the inputted complex number data, and outputs tothe correlation matrix filtering unit 29 as a correlation matrix in thepresent detection cycle.

The target consolidation processing unit 32 extracts the correlationmatrix of the past detection cycle corresponding to the inputteddistance, the relative velocity, the longitudinal position, and thelateral position from the table of FIG. 10 in the memory 21, and outputsto the correlation matrix filtering unit 29.

The correlation matrix filtering unit 29 performs an averaging processof the inputted correlation matrix of the present detection cycle andthe corresponding correlation matrix of the past detection cycle (thedata which was IDBF-processed in the past). Then, the correlation matrixfiltering unit 29 outputs the obtained averaged correlation matrix tothe direction detection unit 30.

According to the process described above, the range of the detectiondirection can be narrowed when the spectrum of the MUSIC is computed inthe direction detection unit 30. Thus, compared to the first, second,and third embodiments, the resolution can be further enhanced.

Furthermore, according to the above described configuration, regardingthe direction detection unit 30, the reception wave divided intoreflection components for each target cluster is hypothetically receivedin the correlation matrix used in the eigen value computation.Therefore, even if the received reception wave includes a reflectioncomponent from a number of targets which is equal to or exceeded by, forexample, the number of reception antennas and the number of subarrays,the eigen value computation can be carried out without any errors.

Furthermore, in the fourth embodiment, a configuration may be made inwhich the IDBF-processed complex number data of the beat frequency forwhich a peak value was detected may be stored with respect to the tableshown in FIG. 10 instead of the correlation matrix.

In this configuration in which the complex number data is stored,similar to the first embodiment, when the correlation matrix filteringunit 29 performs an averaging process of the correlation matrix of thepresent detection cycle and the correlation matrix of the past detectioncycle for each target cluster, the correlation matrix computation unit28 computes the correlation matrix from the complex number data of thepast detection cycle read from the memory 21.

Heretofore, the first, second, third and fourth embodiments have beendescribed based on a configuration used in the FMCW-type radar shown inFIG. 1. However, an application to other antenna configurations of anFMCW-type is also possible.

In addition, an application is possible to a format other than anFMCW-type such as a multi-frequency CW and a pulse radar.

Furthermore, the fourth embodiment was described with, the MUSIC Method,which is a super-resolution algorithm, as an example of the directiondetection unit. However, it is also possible to similarly create acorrelation matrix (or a covariance matrix) and apply a configuration tothe present invention, which is an algorithm based on the principle thatthe more noise is removed from this portion, the more accurate thedetection becomes.

Furthermore, a program executing an operation of the signal processingunit 20 shown in FIG. 1, FIG. 15, FIG. 18, FIG. 21, and FIG. 23 may berecorded in a recording medium which can be read by a computer. Theprogram recorded to this recording medium may then be read by a computersystem, and may be executed to perform a signal processing which detectsthe direction based on a reception wave. Incidentally, the “computersystem” here includes hardware such as OS and peripheral devices. Inaddition, the “computer system” includes a www-system which possesses anenvironment to provide websites (or, an environment for displaying). Inaddition, a “recording medium which can be read by a computer” indicatesa transportable medium such as a flexible disc, an optical magneticdisc, a ROM, a CD-ROM, and the like, as well as a memory device such asa hard disc which is embedded in a computer system. Furthermore, a“recording medium which can be read by a computer” also indicates thosewhich retain a program for a certain period of time such as a networklike an internet, a server when a program is transmitted via atransmission line such as a telephone line, or a volatile memory (RAM)inside a client computer system.

In addition, the program may be transmitted to another computer systemfrom a computer system which stores this program inside a memory deviceand the like, to another computer system through a transmission mediumor a transmission wave inside a transmission medium. Here, a“transmission medium” transmitting the program includes a medium havingan operation of transmitting information, such as a network(communication network) like the internet, or a communication line(communication wire) such as a telephone line. In addition, the programmay be such that a part of the above described operation is executed.Furthermore, the program may be a so-called difference file (differenceprogram) which executes the above described operation in combinationwith a program already recorded in the computer system.

Fifth Embodiment

Hereinafter, a fifth embodiment of an electronic scanning type radardevice (FMCW type milliwave radar) according to the present invention isdescribed with reference to the diagrams. FIG. 26 is a block diagramshowing an example of a configuration of the fifth embodiment.

In this diagram, the electronic scanning type radar device according tothe fifth embodiment includes a reception antenna 111˜11 n, a mixer(beat signal generation unit) 161˜16 n, a transmission antenna 103, adistributor 104, a filter 151˜15 n, a SW (switch) 106, an ADC (A/Dconverter) 107, a control unit 108, a triangular wave generation unit109, a VCO 110, and a signal processing unit 120.

The signal processing unit 120 includes a memory (memory unit) 121, afrequency resolution processing unit 122, a peak detection unit 123, apeak combination unit 124, a distance detection unit 125, a velocitydetection unit 126, a pair confirmation unit 127, a correlation matrixcomputation unit 128, a direction detection unit 130, an eigen valuecomputation unit 131, and a determination unit 132.

Next, an operation of the electronic scanning type radar deviceaccording to the fifth embodiment is described with reference to FIG.26.

The reception antenna 111˜11 n receives a reflection wave, i.e., areception wave, which comes from a target at which a transmission wavereflects.

Each of the mixers 161˜16 n mixes a transmission wave, transmitted bythe transmission antenna 103, and a signal obtained by an amplifieramplifying a reception wave received by each of the reception antennas111˜11 n. Thus, each of the mixers 161˜16 n generates a beat signalcorresponding to each difference in frequency.

The transmission antenna 103 transmits to a target, a transmission wave,which is a transmission signal obtained by the VCO (Voltage ControlledOscillator) 110 frequency-modulating a triangular wave signal generatedby the triangular wave generation unit 109.

The distributor 104 distributes a frequency-modulated transmissionsignal from the VCO 110 to the mixers 161˜16 n and to the transmissionantenna 103.

Each of the filters 151˜15 n executes a band limitation on beat signalsCh1˜Chn, each of which were generated respectively by the mixers 161˜16n, corresponding to each reception antenna 111˜11 n. In this way, eachof the filters 151˜15 n outputs the band-limited beat signal to the SW(switch) 106.

The SW 106 outputs to the ADC (A/D converter) 107, a beat signal ofCh1˜Chn corresponding to each reception antennas 111˜11 n which traveledthrough each of the filters 151˜15 n corresponding to a sampling signalentered by the control unit 108, switching in succession.

The ADC 107 converts the beat signals of Ch1˜Chn, corresponding to eachof the reception antennas 111˜11 n and entered by the SW 106 insynchrony with the sampling signal, to a digital signal by performing anA/D conversion in synchrony with the sampling signal. The ADC 107 alsostores the digital signal in series into a wave form memory region ofthe memory 121 of the signal processing unit 120.

The control unit 108 includes a micro computer and the like. The controlunit 108 controls the overall electronic scanning type radar deviceshown in FIG. 26 based on a control program stored in a ROM, notdiagramed, and the like.

<Principle of Detecting the Distance, Relative Velocity, and Angle(Direction)>

Next, the principle of detecting a distance between the electronicscanning type radar device and a target, a relative velocity, and anangle (direction) is briefly described using FIGS. 27A and 27B. Thisprinciple is utilized by the signal processing unit 120 in the fifthembodiment.

FIGS. 27A and 27B show a transmission signal, which was obtained by theVCO 110 frequency-modulating a signal generated by the triangular wavegeneration unit 109 shown in FIG. 26, and a condition in which thetransmission signal is reflected from the target and is entered as areception signal. The example in FIGS. 27A and 27B shows an instance inwhich there is one target.

As FIG. 27A indicates, a reception signal, which is a reflection wavefrom a target, is received, with respect to the transmitted signal, witha lag in the right direction (direction of time lag) in proportion tothe distance from the target. In addition, the reception signalfluctuates in the longitudinal direction (frequency direction) withrespect to the transmission signal in proportion to the relativevelocity with respect to the target. Furthermore, after the frequencymodulation (such as a Fourier transform, DTC, Hadamard transform, andwavelet transformation) of the beat signal obtained in FIG. 27A, thesignal has a peak value in each of the ascending region and thedescending region, as shown in FIG. 27B, when there is one target. Here,the horizontal axis of FIG. 27B represents the frequency, and thevertical axis represents the intensity.

The frequency resolution processing unit 122 performs a frequencyresolution on each of the ascending portion (ascending) and thedescending portion (descending) of the triangular wave from the sampleddata of the beat signal stored in the memory 121. For example, thefrequency resolution processing unit 122 performs a frequency modulationinto a discrete time by, for example, a Fourier transform.

As a result, in the ascending portion and the descending portion, agraph of the signal level for each beat frequency, which wasfrequency-resolved in each of the ascending portion and in thedescending portion, is obtained, as shown in FIG. 27B.

Then, the peak detection unit 123 detects the peak value from a signallevel for each beat frequency shown in FIG. 27B, and detects theexistence of a target. At the same time, the peak detection unit 123outputs the beat frequency (both the ascending portion and thedescending portion) of the peak value as a target frequency.

Next, the distance detection unit 125 computes the distance fromEquation (11) shown below from the target frequency fu of the ascendingportion and a target frequency fd of the descending portion inputtedfrom the peak combination unit 124.(Equation 11)r={C·T/(2·Δf)}·{(fu+fd)/2}  (11)

Further, the velocity detection unit 126 computes the relative velocityfrom Equation (12) show below from the target frequency fu of theascending portion and the target frequency fd of the descending portioninputted from the peak combination unit 124.(Equation 12)v={C/(2·f0)}·{(fu·fd)/2}  (12)

In the above equations for computing the distance r and the relativevelocity v,

-   -   C: optical velocity    -   Δf: width of the frequency modulation of the triangular wave    -   f0: central frequency of the triangular wave    -   T: modulation time (ascending portion/descending portion)    -   fu: target frequency in the ascending portion    -   fd: target frequency in the descending portion

Next, the reception antenna 111˜11 n according to the fifth embodimentis an array-type antenna which is placed at an interval d, as shown inFIG. 28.

An incoming wave from a target (incident wave, which is a reflectionwave from the target with respect to the transmission wave transmittedby the transmission antenna 103) enters the reception antenna 111˜11 nfrom a direction at an angle of θ degrees from the axis perpendicular tothe surface of the antenna which is lined up.

At this time, the incoming wave is received by the reception antenna111˜11 n at the same angle.

A phase difference “d_(n-1)·sin θ,” which is obtained by this same anglesuch as the angle θ and the interval d between each antenna, occursbetween each adjacent antenna.

This phase difference can be used to perform a digital beam forming(DBF), which is an additional Fourier transform, in the antennadirection, of the value which underwent a frequency resolutionprocessing for each antenna in the temporal direction. The phasedifference can also be used to detect the angle θ in a signal processingof a super resolution algorithm and the like.

<Signal Processing of a Reception Wave by the Signal Processing Unit120>

Next, the memory 121 stores a time-series data (the ascending portionand the descending portion), which was obtained by A/D modulating thereception signal by the ADC 107 with respect to the wave form storingregion, so that each time-series data corresponds to each antenna 111˜11n. For example, when 256 pieces are sampled in each of the ascendingportion and the descending portion, 2×256(pieces)×(number of antennas)numbers of data are stored in the wave form storing region.

The frequency resolution processing unit 122 outputs a frequency pointindicating a beat frequency, and also outputs a complex number data ofthe beat frequency. The frequency point is obtained by performing aFourier transform, for example, and modulating each beat signalcorresponding to each of Ch1˜Chn (each antenna 111˜11 n) into afrequency at a predetermined resolution performance. For example, wheneach of the ascending portion and the descending portion for eachantenna has 256 pieces of sampled data, the beat signal is modulatedinto a beat frequency as a frequency region data of the complex numberfor each antenna. Thus, the beat signal becomes 128 pieces of complexnumber data (2×128 pieces×data for the number of antennas) for each ofthe ascending portion and the descending portion. In addition, the beatfrequency is indicated by the frequency point.

Here, the only difference between each of the complex number data foreach antenna is the phase difference which depends on the angle θ. Theabsolute value (such as the reception intensity or the amplitude) ofeach complex number data on the complex plane is equal.

The peak combination part 124 selects the target frequency and detectsthe existence of a target for each beat frequency by detecting a beatfrequency, which has a peak value exceeding a predetermined value, froma peak of the signal intensity (or the amplitude) using a complex numberdata with respect to the peak value of each intensity for the ascendingregion and the descending region of the triangular wave of the beatfrequency which was frequency-modulated.

Therefore, the peak detection unit 123 can detect each peak value of thespectrum as a beat frequency, in other words, an existence of a targetwhich depends on the distance, by converting the complex number data foreither one of the antennas, or the added value of the complex numberdata for all of the antennas, into a frequency spectrum. By the additionof the complex number data for all of the antennas, the noise element isaveraged, and the S/N ratio increases.

The peak combination unit 124 combines the beat frequency and its peakvalue, entered by the peak detection unit 123 and shown in FIG. 29, witha beat frequency of each ascending region and the descending region andits peak value, in a matrix fashion in a round-robin matter. In otherwords, the peak combination unit 124 combines all of the beatfrequencies in each of the ascending region and the descendingdirection. Thus, the peak combination unit 123 outputs, in series, tothe distance detection unit 125 and the velocity detection unit 126, andconfirms the combination at the pair confirmation unit 127. Here, thehorizontal axis of FIG. 29 indicates the frequency point of the beatfrequency, while the vertical axis indicates the level (intensity) ofthe signal.

The distance detection unit 125 computes the distance r to the targetbased on a value obtained by adding the beat frequency of thecombination for each ascending region and the descending region, whichare inputted in series.

Further, the velocity detection unit 126 computes the relative velocityv with respect to the target by the difference in the beat frequency ofthe combination for each ascending region and the descending region,which are inputted in series.

In addition, the correlation matrix computation unit 128 selects thebeat frequency, which underwent a frequency resolution by the frequencyresolution processing unit 122, according to the frequency point of thebeat frequency of the pair whose combination was confirmed. Thus, thecorrelation matrix computation unit 128 generates a correlation matrixcorresponding to the beat frequency of either one of the ascendingportion and the descending portion (in the fifth embodiment, thedescending portion) regarding this combination.

<Super-Resolution Algorithm in the Estimation of the Arrival Directionof an Incoming Wave>

Next, a super-resolution algorithm estimating the arrival direction ofan incoming wave according to the correlation matrix computation unit128, the eigen value computation unit 131, the determination unit 132,and the direction detection unit 130, is described with MUSIC as anexample with reference to FIG. 30. FIG. 30 is a flowchart describing theflow of the operating process of a general MUSIC Method. Since theprocess of the MUSIC Method itself is used in general (for example, inNon-Patent Documents 1 and 2, or, Patent Documents 3, 4, 8, and 9), onlythe aspects of the MUSIC Method which are necessary in the fifthembodiment are described.

The frequency resolution processing unit 122 reads in the beat signal ofthe reception wave stored in the memory 121 (step S1101), and performs afrequency-modulation on the beat signal for each antenna (step S1102).

Further, as described above, the correlation matrix computation unit 128reads in the complex number frequency region data (hereinafter referredto as complex number data) by making a selection from the frequencyresolution processing unit 122. The complex number data has undergone afrequency resolution, and corresponds to the frequency point of thetarget in the descending region for which a pair has been confirmed bythe pair confirmation unit 127. In addition, regarding the descendingregion, the correlation matrix computation unit 128 generates acorrelation matrix indicating the correlation for each antenna (stepS1103).

The generation of the correlation matrix by the correlation matrixcomputation unit 128 in step S1103 is conducted, for example, accordingto the methods shown in FIGS. 31A and 31B. The methods shown in FIGS.31A and 31B are briefly described below.

According to the method shown in FIG. 31A, the correlation matrixcomputation unit 128 generates a correlation matrix (complex correlationmatrix) based on the bare complex number data (step S1103_1), andprocesses with a forward-only spatial average (Forward Spatial AveragingMethod) or a forward-and-backward spatial average (Forward-BackwardSpatial Averaging Method) (step S1103_2).

Spatial averaging refers to a process in which the number of antennas inthe array of the original reception antennas is divided into subarrayswhich has a lesser amount of antennas, and the subarrays are averaged.The phase relation of waves having a correlation differs according tothe position at which the wave was received. Thus, according to thisbasic principle of spatial averaging, the correlation matrix is obtainedby moving the reception point in an appropriate manner. In this way, thebasic principle of spatial averaging is such that the correlation of thecorrelated interference wave is restrained due to the effect of theaveraging process. In general, the averaging is conducted by taking outa plurality of subarrays having the same alignment from the overallarray of reception antennas without moving the array of receptionantennas, and then obtaining the average of each correlation matrix.

For example, as shown in FIG. 32, when the array of reception antennas111˜111 n is such that there are nine antennas (n=9), the correlationmatrix computation unit 128 obtains the backward correlation matrixCR^(b) _(f) in the latter equation (6) with respect to the correlationmatrix CR^(f) _(f) in the forward equation (5) indicated below. Thus,the correlation matrix computation unit 128 carries out an averagingprocedure of the forward/backward elements by averaging thecorresponding elements in the correlation matrix in equation (5) and thebackward correlation matrix in equation (6) according to the followingequation (13).(Equation 13)CR ^(fb) _(f)=(CR ^(f) _(f) +CR ^(b) _(f))/2  13)

In this way, the correlation matrix computation unit 128 divides thecorrelation matrix CR^(fb) _(f), obtained by the forward/backwardaveraging process, into subarrays, and computes an average. Thus, thecorrelation matrix computation unit 128 obtains a correlation matrix Rxxwhich is used to estimate the arrival direction of the reception wave.In other words, the correlation matrix obtained by the forward/backwardspatial averaging process can be expressed as follows by Equation (14).(Equation 14)Rxx=(CR ^(fb1) _(f) +cR ^(fb2) _(f) +cR ^(fb3) _(f))/3  (14)

Here, the correlation matrix computation unit 128 obtains thecorrelation matrix Rxx by dividing the nine reception antennas 111˜119into three subarrays each of which including seven antennas 111˜117,112˜118, and 113˜119, and by averaging the corresponding elements ofeach matrix in the subarray.

Meanwhile, in the case of the forward spatial averaging, the matricesfrom V₁₁ to V₉₉ can be kept as the matrices from W₁₁ to W₉₉ in equation(5). Thus, it is not necessary to average each element as shown, forexample, in equation (15).(Equation 15)V ₁₁=(W ₁₁ +W ₉₉)/2  (15)

Regarding the use in which the arrival direction of the reception waveregarding the radar is estimated, all of the incoming reception wavesare reflection waves caused by the transmitted transmission wavereflecting from the target. Therefore, the data of the reception wavesreceived by each antenna exhibits a strong correlation with one another.Thus, the results of the eigen value computation in the latter phase arenot obtained accurately. In this way, spatial averaging has an effect ofrestraining the correlation, extracting a self correlation, andaccurately estimating the direction of the incoming wave.

Next, the correlation matrix computation unit 128 performs a unitaryconversion in order to convert the correlation matrix of complex data,which underwent a spatial averaging process as described above, into acorrelation matrix of real numbers.

Here, by converting into a correlation matrix of real numbers, the eigenvalue computation in a subsequent step which has the heaviestcomputation load can be executed using real numbers only. In this way,the computation load can be greatly reduced.

Meanwhile, FIG. 31B shows a variation in which the eigen valuecomputation in the subsequent step is executed using complex numberswithout converting into a correlation matrix of real numbers byperforming a unitary conversion as indicated in FIG. 31A.

Further, in step S1103, regarding the correlation matrix Rxx obtained bythe step S1103_3 in FIG. 31A and the step S1103_2 in FIG. 31B, thevalues of each element can be normalized (i.e., divided by the maximumvalue) based on the maximum value of the correlation matrix (or thediagonal element of the correlation matrix).

Next, the eigen value computation unit 131 computes the eigen value ofthe correlation matrix Rxx obtained in step S1103 and its correspondingeigen vector as an eigen value λ and an eigen vector e which satisfiesthe following characteristic equation, outputs to the directiondetection unit 130, and outputs the eigen value λ to the determinationunit 132 (step S1104).(Equation 16)Rxxe=λe  (16)

Then, based on the eigen value λ obtained above by the eigen valuecomputation unit 131, the determination unit 132 estimates the number ofincoming waves necessary to remove the signal component vector (stepS1105).

Here, the determination unit 132 performs the above estimation of theincoming wave according to the incoming wave estimation process,described later.

Next, the direction detection unit 130 generates a spectrum of angles bycomputing an inner product of a vector with only the noise componentsafter removing the signal vector, and a vector for each direction andangle which is predetermined internally (step S1106). As a result, it ispossible to associate a null with a directional characteristic to thearrival direction of the incoming wave.

Further, the direction detection unit 130 detects a peak from thespectrum of angles which exceeds a predetermined threshold value. Inthis way, the direction detection unit 130 detects the peak and computesthe direction of the incoming wave (angle θ) (step S1107).

In addition, the direction detection unit 130 can make a conversion to aposition in the lateral direction with respect to the vertical axis ofthe array of antennas of the electronic scanning type radar device basedon the angle (i.e., the arrival direction of the reception wave) and thedistance computed by the distance detection unit 125.

A standard MUSIC Method has been described above. In the MUSIC spectrumcomputation in step S1106, it is possible to use a method called theRoot-MUSIC Method which computes a solution from the root of thepolynomial, instead of a type searching with a direction vector.

In addition, after the step S1107 in FIG. 30, it is possible to add aprocess computing the received electronic power and deleting anunnecessary wave (data of an unnecessary reception wave).

In other words, the determination unit 132 compares the electronic powerindicated in the diagonal component of the matrix S in the followingequation with a predetermined threshold value, and detects whether ornot the electronic power exceeds the threshold value. Further, thedetermination unit 132 has a process which makes a determination ofnecessary reception wave when the electronic power exceeds the thresholdvalue, and, meanwhile, makes a determination of unnecessary receptionwave when the electronic power is less than or equal to the thresholdvalue.(Equation 17)S=(A ^(H) A)⁻¹ A ^(H)(Rxx−σ ² I)A(A ^(H) A)⁻¹  (17)

Here, S indicates the correlation matrix of the signal of the receptionwave, A indicates the directional matrix, A^(H) indicates the conjugatetranspose matrix of A, I indicates the unit matrix, Rxx indicates thecorrelation matrix computed by the correlation matrix computation unit128, and σ² indicates the dispersion of the noise vector.

By adding the process, described above, of computing the receivedelectronic power and deleting an unnecessary wave, it is possible todelete the unnecessary incoming reception wave, when the number ofreception waves was overestimated in the estimation of the number ofreception waves in step S1105. Therefore, it is possible to retain amargin of the setting of the threshold value λth and the threshold valueλth′ in the estimation process of the number of incoming waves describedbelow (in other words, even if each threshold value is not set rigidly,the reception wave that does not have an adequate reception electricpower is deleted).

<Incoming Wave Estimation Process>

Next, an incoming wave estimation process in step S1105 of FIG. 30 isdescribed with reference to FIG. 33. This incoming wave estimationprocess is a process characteristic of the fifth embodiment. The processof estimating the number of incoming waves, shown in the flowchart inthis FIG. 33, is a process in which primarily the determination unit 132in FIG. 26 uses the eigen value inputted from the eigen valuecomputation unit 131.

As already described in the flowchart in FIG. 30, at the time when stepS1105 in FIG. 30 begins to be executed, the peak combination unit 124has detected the target, and the eigen value computation unit 131 hasalready computed the eigen value and the eigen vector of the correlationmatrix Rxx.

Therefore, the determination unit 132 assumes that there is at least oneincoming wave, and therefore enters the number 1 into the number ofincoming waves L (step S1401).

Then, the determination unit 132 detects, from among the eigen valuesobtained by the correlation matrix, a maximum eigen value λa which has amaximum value. The determination unit 132 next performs a normalizationof the eigen value λx by dividing all of the eigen values λx (x=1, 2, 3)by the maximum eigen value λa (determining the ratio between the maximumeigen value λa and all of the eigen values λx which includes thismaximum eigen value λa). In this way, the determination unit 132 sets λy(y=1, 2, 3) as the normalized eigen value (step S1402). At this time,the determination unit 132 rearranges the normalized eigen values λyfrom the largest to the smallest.

Next, the determination unit 132 compares in series, the predeterminedthreshold λth and the eigen value λy, in the order from the largest ofthe eigen value λy (step S1403). Then, when the determination unit 132detects that the eigen value λy is greater than or equal to thethreshold value λth, the determination unit 132 proceeds the operationto step S1404.

Then, the determination unit 132 increments the number of incoming wavesL (by adding 1), and returns the operation to step S1403.

Meanwhile, when the determination unit 132 detects that the eigen valueλy is less than the threshold value λth, it is no longer necessary tolater make a comparison between the eigen value λy and the thresholdvalue λth (because the subsequent eigen value λy is smaller than theeigen value λy which is presently being compared). Therefore, thedetermination unit 132 proceeds the operation to step S1405 (stepS1403).

Then, the determination unit 132 confirms the present number of incomingwaves L as the detected number of incoming waves L. The determinationunit 132 next outputs this confirmed number of incoming waves L to thedirection detection unit 130 (step S1405).

In this process estimating the number of incoming waves, thedetermination unit 132 performs the process from step S1401 to S1405described above, every time an eigen value is inputted from the eigenvalue computation unit 131.

In addition, as shown in the flowchart in FIG. 34, before the process ofestimating the number of incoming waves is executed, the determinationunit 132 detects the maximum eigen value λa from the eigen value λxinputted from the eigen value computation unit 131.

Further, the determination unit 132 detects whether or not this detectedmaximum eigen value λa is greater than or equal to a predeterminedthreshold λmax (step S1400). When the determination unit 132 detectsthat the maximum eigen value λa is greater than or equal to thethreshold value λmax, the determination unit 132 performs step S1401shown in FIG. 33 and the steps subsequent to step S1401 in the processfor determining the number of incoming waves. Meanwhile, when thedetermination unit 132 detects that the maximum eigen value λa is lessthan the threshold value λmax, the determination unit 132 does notexecute the process for estimating the number of incoming waves. Thus,the determination unit 132 does not output the number of incoming wavesL to the direction detection unit 130.

In other words, even in embodiments such that an eigen value is obtainedfrom a correlation matrix of the entire frequency point or within arange of the frequency point, it is possible to cancel (halt) theprocess of estimating the number of incoming waves during the estimationof the number of incoming waves. Thus, even if the level of reception islow due to the influence of multipass on the road surface, it ispossible to avoid making an erroneous estimation of the number ofincoming waves.

Next, another process for estimating a number of an incoming wave isdescribed with reference to the flowchart shown in FIG. 35. This FIG. 35is different from the flowchart shown in FIG. 33 and FIG. 34 in that anormalization is not made after the eigen value is computed. Instead, asdescribed in the description of the correlation matrix computation unit128, a configuration may be made such that the correlation matrixcomputation unit 128 performs a normalization by dividing each elementof the correlation matrix Rxx by the maximum value of the diagonalelement among each element of the correlation matrix Rxx, and then, theeigen value computation unit 131 computes the eigen value and the eigenvector.

In addition, instead of normalizing the correlation matrix Rxx at thecorrelation matrix computation unit 128, the normalization process maybe carried out before the eigen value computation unit 131 computes theeigen value, and then, the eigen value and the eigen vector may becomputed.

As a result, the accuracy of the floating point calculation of the eigenvalue computation increases. In addition, it is possible to reduce thenumber of computations necessary for the conversion of the arithmeticalgorithm (such as the Jacobi Method and the QR Method) of the eigenvalue and the eigen vector. In this way, it is possible to reduce thetime spent on the calculation. Further, it is not necessary to normalizethe eigen value in the process for estimating the number of incomingwaves. In addition, among each element of the correlation matrix Rxx,when the maximum value of all of the elements including the diagonalelement is set to be the standard for the normalization, thenormalization process of the eigen value in step S1402 shown in FIG. 33may be executed before the step S1501 shown in FIG. 35.

In either case, the eigen value λx (x=1, 2, 3, . . . ) computed by thenormalized correlation matrix is inputted into the determination unit132, and the process for determining the number of incoming waves shownin the flowchart in FIG. 35 begins. At this time, the determination unit132 resets the number of incoming waves L to 0.

The determination unit 132 sorts the inputted eigen value λx from thelargest to the smallest. Then, the determination unit 132 makes acomparison between each eigen value λx and the predetermined thresholdvalue λth′ in the order from the largest eigen value λx to the smallest(step S1501).

At this time, when the determination unit 132 detects that the eigenvalue λx is greater than or equal to the predetermined threshold valueλth′, the determination unit 132 proceeds the operation to step S1502.Meanwhile, when the determination unit 132 finds that the eigen value λxis less than the predetermined threshold value λth′, the determinationunit 132 proceeds the operation to step S1503.

Further, when the determination unit 132 finds that the eigen value λxis greater than or equal to the predetermined threshold value λth′, thedetermination unit 132 increments the number of incoming waves L (stepS1502), and returns the operation to step S1501.

Further, when the eigen value λx is less than the predeterminedthreshold value λth′, the determination unit 132 confirms the presentnumber of incoming waves L as the estimated number of incoming waves,and outputs to the direction detection unit 130 (step S1503).

In this process for estimating the number of incoming waves, thedetermination unit 132 executes the above described process from stepS1501 to step S1503 every time an eigen value is inputted from the eigenvalue computation unit 131.

Furthermore, as shown in FIG. 36, it is possible to place a step S1500before the comparison process of step S1501 in the flowchart shown inFIG. 35. In the step S1500, the peak value detected by the peakdetection unit 123 after the frequency resolution is compared with thepredetermined threshold value PEAK-th.

Further, the determination unit 132 detects whether or not the peakvalue inputted from the peak detection unit 123 is greater than or equalto a predetermined threshold PEAK-th (step S1500). When thedetermination unit 132 detects that the peak value is greater than orequal to the threshold value PEAK-th, the determination unit 132performs step S1501 shown in FIG. 35 and the steps subsequent to stepS1501 in the process for determining the number of incoming waves.Meanwhile, when the determination unit 132 detects that the peak valueis less than the threshold value PEAK-th, the determination unit 132does not execute the process for estimating the number of incomingwaves. Thus, the determination unit 132 does not output the number ofincoming waves L to the direction detection unit 130.

In other words, even in embodiments such that an eigen value is obtainedfrom a correlation matrix of the entire frequency point or within aspecific range of the frequency point, it is possible to cancel (halt)the process of estimating the number of incoming waves during theestimation of the number of incoming waves. Thus, even if the level ofreception is low due to the influence of multipass on the road surface,it is possible to avoid making an erroneous estimation of the number ofincoming waves. Moreover, as shown in FIG. 37, instead of the step S1500in FIG. 36, it is possible to place a step S1500 in which the maximumvalue of the diagonal element of the obtained correlation matrix iscompared with a predetermined threshold value.

FIGS. 38A, 38B, 38C, and FIGS. 39A and 39B are graphs showing acondition in which the distribution of the eigen values actuallyfluctuates for each distance (for each beat frequency). FIGS. 38A, 38B,and 38C present the instance in which one wave has arrived (the numberof incoming wave being 1). FIGS. 39A and 39B present the instance inwhich two waves have arrived (the number of incoming waves being 2).

Here, the horizontal axis of FIGS. 38A and 39A indicates the distance,while the vertical axis indicates the eigen value. In addition, thehorizontal axis of FIGS. 38B and 39B indicates the distance, while thevertical axis indicates the value obtained by normalizing the othereigen value λx with the maximum eigen value λa.

FIG. 38A and FIG. 39A indicate that, in an area within a distance ofapproximately 65 m and 80 m from the target, a region exists such thatthe eigen value becomes small due to multipass.

In addition, as shown in FIG. 38B and FIG. 39B, even if the value isnormalized, the fluctuation of the normalized value itself becomeslarge, and an erroneous estimation of the incoming waves may be madewhen the incoming wave estimation is conducted at a region under theinfluence of multipass.

Therefore, according to the processes of step S1400 of FIG. 34, stepS1500 of FIG. 36, and step S1500 of FIG. 37, a configuration isintroduced in which an incoming wave estimation is not made. Thus, theestimation of the number of incoming waves and the detection of thedirection according to this correlation matrix may be cancelled.Therefore, an erroneous detection result of the direction is notcalculated.

FIG. 38C shows the value of the eigen value λx at a distance of 100 (m)in FIG. 39A, in which the number of incoming wave is 1. Thus, FIG. 38Cshows the difference between the values of the eigen value λ1 in thesignal space and the eigen value in another noise space.

Conventionally, the estimation of the incoming wave was conducted bysetting a threshold value Th for each distance by using the eigen valuesof FIG. 38A and FIG. 39A. However, in the fifth embodiment, the eigenvalue is normalized, and a comparison with the threshold value Th ismade, as shown in FIG. 38B and FIG. 39B. Therefore, as alreadydescribed, the threshold value λth (or the threshold value λth′) is setas one value which is uniform for all distances. Thus, a comparison ismade with the eigen value for all distances. Therefore, the estimationof the number of incoming waves is made easily.

In addition, when the estimation of the number of incoming waves cannotbe conducted, the direction detection unit 130 copes with this situationby way of a method estimating the present distance based on the pastdistance, the relative velocity, and the direction.

Sixth Embodiment

Hereinafter, an electronic scanning type radar device according to asixth embodiment of the present invention is described with reference toFIG. 40. FIG. 40 is a block diagram showing an example of aconfiguration of a signal processing unit 120 of the electronic scanningtype radar device according to the sixth embodiment.

The same reference numeral is used for the configuration which issimilar to the fifth embodiment shown in FIG. 26. Hereinafter, theaspects which are different from the fifth embodiment are described.

According to this sixth embodiment, different from the fifth embodiment,an estimation of a direction is first made using a DBF (Digital BeamForming) which has a lower resolution performance compared to asuper-resolution algorithm such as the MUSIC Method. Next, asuper-resolution algorithm is used to estimate the direction from acorrelation matrix which has undergone an averaging process. The samereference numeral is used for the configuration which is similar to thefifth embodiment shown in FIG. 26. Hereinafter, the aspects which aredifferent from the fifth embodiment are described.

As shown in FIG. 40, a DBF processing unit 133 is provided between thefrequency dissolution processing unit 122 in the fifth embodiment shownin FIG. 26 and the peak detection unit 123. As described above, thesixth embodiment differs from the fifth embodiment in that a directioncan be estimated in advance at the level of each target cluster,although at a comparatively far distance, a fine separation cannot bemade for each target.

Similar to the fifth embodiment, the frequency dissolution processingunit 122 performs a frequency resolution on the inputted beat signal(temporal axis Fourier transform), and outputs a frequency pointindicating the beat frequency and the complex number data to the DBFprocessing unit 133.

Next, the DBF processing unit 133 performs a Fourier transform on theinputted complex number data corresponding to each antenna in thedirection in which the antenna is aligned. In other words, the DBFprocessing unit 133 performs a spatial axis Fourier transform.

Then, the DBF processing unit 133 computes the spatial complex numberdata for each angular channel corresponding to the angular resolution,which, said differently, depends on the angle, and outputs to the peakdetection unit 123 for each beat frequency.

Therefore, the spectrum, indicated by the spatial complex number data(with a unit of beat frequency) for each angular channel outputted fromthe DBF processing unit 133, depends on the estimation of the arrivaldirection of the reception wave by the beam scanning resolution.

In addition, since a Fourier transform is conducted in the direction inwhich the antenna is aligned, the same effect can be obtained as whenthe complex number data is added between the angular channels.Furthermore, the S/N ratio of the complex number data for each angularchannel is improved. Thus, the accuracy with which the peak value isdetected can be enhanced in a manner similar to the fifth embodiment.

As in the fifth embodiment, the above described complex number data andthe spatial complex number data are computed in both the ascendingregion and the descending region of the triangular wave.

Next, the peak detection unit 123 performs a detection of the peak valuebased on the spectrum intensity indicated by the spatial complex numberdata for each angular channel which is inputted. The peak detection unit123 then outputs to the peak combination unit 124. The peak detectionunit 124 also outputs the angular channel number (or region) in whichthe target cluster exists, as information of the direction with a rough(low) resolution level, to the direction detection unit 130. Byoutputting an angular channel in which a target exists, as shown in FIG.41A and FIG. 42A, it is possible to narrow down the detection range ofthe direction to a narrow angular range when the MUSIC spectrum iscomputed, compared to the above instance when there is no information onthe angular channel. Therefore, it is possible to enhance the resolutionof the spectrum computation of MUSIC.

Here, FIG. 41A and FIG. 42A shows an instance in which a Fouriertransform of 16 bites was conducted in the direction of the channel (inthe direction of the antenna) so that the angular dependency Ch(channel) after the DBF becomes 15Ch. Here, in the MUSIC process, whenthe value of the spectrum intensity has exceeded the DBF level thresholdvalue in the range of 4Ch consecutive Ch (angles), the directiondetection unit 130 makes a setting as the above described narrow range,and performs an analysis of the detection range of the direction in thisangular range with a high level of accuracy.

Further, in FIG. 42A, there are two different groups of the spectrumintensity values which exceed the DBF level threshold value in 4Chconsecutive angular range. Therefore, in each range (the angular rangesof Ch3˜Ch6 and Ch10˜Ch13), the direction detection unit 130 narrows downthe angular range for which the MUSIC spectrum is computed.

Similar to the fifth embodiment, the peak combination unit 124 combinesa beat frequency in the ascending region and the descending region andits peak value, and outputs to the distance detection unit 125 and thevelocity detection unit 126. The combination is confirmed by the paircombination unit 127.

At this time, the peak combination unit 124 uses the angular channel asthe information for the combination. Thus, the peak combination unit 124outputs the combination of the beat frequency in the ascending regionand the descending region to the distance detection unit 125 and thevelocity detection unit 126.

In FIGS. 41A, 41B, 41C, and FIGS. 42A, 42B, and 42C, the horizontal axisshows the Ch number of the angular channel, while the vertical axisshows the spectrum intensity for each Ch which was computed during theDBF process.

Seventh Embodiment

Hereinafter, an electronic scanning type radar device according to aseventh embodiment of the present invention is described with referenceto FIG. 43. FIG. 43 is a block diagram showing an example of aconfiguration of the electronic scanning type radar device according tothe seventh embodiment.

According to this seventh embodiment, similar to the sixth embodiment,an estimation of a direction is first made using a DBF (Digital BeamForming) which has a lower resolution performance compared to asuper-resolution algorithm such as the MUSIC Method. In this way, theangular range of the target is narrowed, an IDBF (inverse DBF, in otherwords, an inverse spatial axis Fourier transform) is performed, thusreconverting to the complex number data of a temporal axis. Therefore,the seventh embodiment is configured so that the accuracy of theestimation of the direction conducted in the subsequent super-resolutionalgorithm is enhanced. The same reference numeral is used for theconfiguration which is similar to the fifth embodiment shown in FIG. 26.Hereinafter, only the aspects which are different from the fifthembodiment are described.

The seventh embodiment is configured so that a Ch (Channel) deletingunit 134 and an IDBF processing unit 135 are added to the sixthembodiment.

The DBF processing unit 133 performs, similar to the sixth embodiment, aspatial axis Fourier transform, and outputs the spatial complex numberdata to the peak detection unit 123, and outputs to the Ch deleting unit134 as well.

Here, in the seventh embodiment in the direction in which the receptionantennas are aligned, as shown in FIG. 41A, the DBF processing unit 133performs a spatial axis Fourier transform based on a 16-pointresolution, for instance, and, as a result, creates a spectrum with anangle unit of 15 angular channels, and outputs to the Ch deleting unit134.

Then, the Ch deleting unit 134 selects the spatial complex number datacorresponding to the frequency point of the target in the descendingregion for which a combination was confirmed by the pair confirmationunit 127. In addition, the Ch deleting unit 134 detects whether or notthe level of the spectrum is continuous while being adjacent to thepredetermined angular range, and, whether or not the level of thepredetermined DBF threshold value is exceeded. Furthermore, the Chdeleting unit 134 performs a process converting the spectrum of theangular channel which does not exceed the DBF threshold value to “0,”and thus outputs a narrowed spatial complex number data for each beatfrequency as shown in FIG. 41B.

According to the process described above, when, for example, fouradjacent angular channels have a level which continuously exceeds theDBF threshold value, the Ch deleting unit 134 determines that a targetexists, and leaves the spectrum of these angular channels intact, whileconverting the intensity of a spectrum of another angle to “0.”

Further, the IDBF processing unit 135 performs an inverse spatial axisFourier transform on a spatial complex number data such that thespectrum was narrowed, i.e., only the data of the angular channel regionbeing continuous for the predetermined number of angular channels andexceeding the DBF threshold value is left, and the intensity of the restof the region is converted to “0.” Thus, the IDBF processing unit 135restores the spatial complex number data to a complex number data of atemporal axis, and outputs to the correlation matrix computation unit128.

Furthermore, in order to compute a correlation matrix from the inputtedcomplex number data, the correlation matrix computation unit 128 canobtain a correlation matrix with a good orthogonal characteristic suchthat objects on the roadside and the like are removed and the noiseelement is deleted. FIG. 41C shows an example in which a correlationmatrix is created by the above described method with respect to thetarget cluster of the DBF resolution in FIG. 41B (the term “targetcluster” is used because, in actuality, two or more targets may exist),and the target is divided even further by a super-resolution algorithm.

In addition, as shown in FIG. 42A, when a reception wave including areflection component from a plurality of target clusters is received,there are a plurality of angular channel ranges, which exceed the DBFlevel at continuous angular channels, in the spatial complex number dataoutputted from the DBF processing unit 133.

Furthermore, regarding the inputted spatial complex number data, withinthe predetermined angular channel range, when the level of the spectrumof the adjacent angular channels continuously exceeds the level of theDBF threshold value, the Ch deleting unit 134 extracts each of theexceeded angular channel region, and converts the intensity of thespectrum outside this angular channel region to “0.” Thus, as shown inFIGS. 42B and 42C, the Ch deleting unit 134 makes a division intoseparate spatial complex number data which is recognized in the angularchannel region.

The Ch deleting unit 134 selects the spatial complex number datacorresponding to the frequency point of the target in the descendingregion for which a combination has been confirmed by the pairconfirmation unit 127, and, after performing the above described Chdeletion, outputs to the IDBF processing unit 135.

In addition, the IDBF processing unit 135 performs an inverse spatialFourier transform on the inputted spatial complex number data, andoutputs the obtained temporal axis complex number data to thecorrelation matrix computation unit 128.

As a result, the correlation matrix computation unit 128 calculates thecorrelation matrix from the inputted complex number data, and outputs tothe eigen value computation unit 131.

The subsequent process for estimating the number of incoming waves issimilar to the process described already and shown from FIG. 33 to FIG.36.

According to the process described above, the range of the detectiondirection can be narrowed when the spectrum of the MUSIC is computed inthe direction detection unit 130. Thus, compared to the fifthembodiment, the resolution can be further enhanced.

Furthermore, according to the above described configuration, regardingthe direction detection unit 130, the reception wave divided intoreflection components for each target cluster is hypothetically receivedin the correlation matrix used in the eigen value computation.Therefore, even if the received reception wave includes a reflectioncomponent from a number of targets which is equal to or exceeded by, forexample, the number of reception antennas and the number of subarrays,the eigen value computation can be carried out without any errors.

In addition, a configuration may be made in which, after the directionof the present target is detected, the direction detection unit 130stores the direction of this target to the memory 121, regards it asinformation of a past cycle after the next direction computation cycle,read it from the memory 121, and in the direction computation cycle,perform a spectrum calculation while prioritizing the angular rangesurrounding the target direction in the past cycle.

Heretofore, the fifth, sixth, and seventh embodiments have beendescribed based on a configuration used in the FMCW-type radar shown inFIG. 26. However, an application to other antenna configurations of anFMCW-type is also possible.

In addition, an application is possible to a format other than anFMCW-type such as a multi-frequency CW and a pulse radar. In addition,according to the seventh embodiment, the estimation of the number ofincoming waves and the detection of the direction were conductedconcerning the correlation matrix corresponding to the beat frequency ofeither one of the ascending portion and the descending portion of thetriangular wave. However, it is possible to perform the estimation ofthe number of incoming waves and the detection of the direction in eachof the ascending region and the descending region, and, perform a peakcombination after detecting the direction. Moreover, the seventhembodiment was described based on the MUSIC Method, which is asuper-resolution algorithm, as an example of the direction detectionunit. However, it is possible to apply the Minimum Norm Method and theESPRIT Method and the like, which performs an eigen expansion in asimilar manner, and is a detection algorithm based on the principle thatthe number of incoming waves is estimated in order to detect thedirection of the incoming wave.

Furthermore, a program executing an operation of the signal processingunit 120 shown in FIG. 26, FIG. 40, and FIG. 43 may be recorded in arecording medium which can be read by a computer. The program recordedto this recording medium may then be read by a computer system, and maybe executed to perform a signal processing which performs a detection ofthe direction and includes a process estimating the number of incomingwaves as shown in FIG. 33 to FIG. 36, in which the number of receptionwaves is estimated. Incidentally, the “computer system” here includeshardware such as OS and peripheral devices. In addition, the “computersystem” includes a www-system which possesses an environment to providewebsites (or, an environment for displaying). In addition, a “recordingmedium which can be read by a computer” indicates a transportable mediumsuch as a flexible disc, an optical magnetic disc, a ROM, a CD-ROM, andthe like, as well as a memory device such as a hard disc which isembedded in a computer system. Furthermore, a “recording medium whichcan be read by a computer” also indicates those which retain a programfor a certain period of time such as a network like an internet, aserver when a program is transmitted via a transmission line such as atelephone line, or a volatile memory (RAM) inside a client computersystem.

In addition, the program may be transmitted to another computer systemfrom a computer system which stores this program inside a memory deviceand the like, to another computer system through a transmission mediumor a transmission wave inside a transmission medium. Here, a“transmission medium” transmitting the program includes a medium havingan operation of transmitting information, such as a network(communication network) like the internet, or a communication line(communication wire) such as a telephone line. In addition, the programmay be such that a part of the above described operation is executed.Furthermore, the program may be a so-called difference file (differenceprogram) which executes the above described operation in combinationwith a program already recorded in the computer system.

Eighth Embodiment

Hereinafter, an eighth embodiment of an electronic scanning type radardevice (FMCW type milliwave radar) according to the present invention isdescribed with reference to the diagrams. FIG. 44 is a block diagramshowing an example of a configuration of the eighth embodiment.

In this diagram, the electronic scanning type radar device according tothe eighth embodiment includes a reception antenna 211˜21 n, a mixer(beat signal generation unit) 261˜26 n, a transmission antenna 203, adistributor 204, a filter 251˜25 n, a SW (switch) 206, an ADC (A/Dconverter) 207, a control unit 208, a triangular wave generation unit209, a VCO 210, and a signal processing unit 220.

The signal processing unit 220 includes a memory (memory unit) 221, afrequency resolution processing unit 222, a peak detection unit 223, apeak combination unit 224, a distance detection unit 225, a velocitydetection unit 226, a pair confirmation unit 227, a correlation matrixcomputation unit 228, a direction detection unit 230, an eigen valuecomputation unit 231, a determination unit 232, and an angular rangesetting unit 250. Here, the angular range setting unit 250 is configuredto estimate the angular range in which a target exists, and is acharacteristic part of the present invention. According to the eighthembodiment, as shown in FIG. 45, the angular range setting unit 250includes the DBF processing unit 233 and the range detection unit 236.

Next, an operation of the electronic scanning type radar deviceaccording to the eighth embodiment is described with reference to FIG.44 and FIG. 45.

The reception antenna 211˜21 n receives a reflection wave, i.e., areception wave, which comes from a target at which a transmission wavereflects.

Each of the mixers 261˜26 n mixes a transmission wave, transmitted bythe transmission antenna 203, and a signal obtained by an amplifieramplifying a reception wave received by each of the reception antennas211˜21 n. Thus, each of the mixers 261˜26 n generates a beat signalcorresponding to each difference in frequency.

The transmission antenna 203 transmits to a target, a transmission wave,which is a transmission signal obtained by the VCO (Voltage ControlledOscillator) 210 frequency-modulating a triangular wave signal generatedby the triangular wave generation unit 209.

The distributor 204 distributes a frequency-modulated transmissionsignal from the VCO 210 to the mixers 261˜26 n and to the transmissionantenna 203.

Each of the filters 251˜25 n executes a band limitation on beat signalsCh1˜Chn, each of which were generated respectively by the mixers 261˜26n, corresponding to each reception antenna 211˜21 n. In this way, eachof the filters 251˜25 n outputs the band-limited beat signal to the SW(switch) 206.

The SW 206 outputs to the ADC (A/D converter) 207, a beat signal ofCh1˜Chn corresponding to each reception antennas 211˜21 n which traveledthrough each of the filters 251˜25 n corresponding to a sampling signalentered by the control unit 208, switching in succession.

The ADC 207 converts the beat signals of Ch1˜Chn, corresponding to eachof the reception antennas 211˜21 n and entered by the SW 206 insynchrony with the sampling signal, to a digital signal by performing anA/D conversion in synchrony with the sampling signal. The ADC 207 alsostores the digital signal in series into a wave form memory region ofthe memory 221 of the signal processing unit 220.

The control unit 208 includes a micro computer and the like. The controlunit 208 controls the overall electronic scanning type radar deviceshown in FIG. 44 based on a control program stored in a ROM, notdiagramed, and the like.

<Principle of Detecting the Distance, Relative Velocity, and Angle(Direction)>

Next, the principle of detecting a distance between the electronicscanning type radar device and a target, a relative velocity, and anangle (direction) is briefly described using FIGS. 46A and 46B. Thisprinciple is utilized by the signal processing unit 220 in the eighthembodiment.

FIGS. 46A and 46B show a transmission signal, which was obtained by theVCO 210 frequency-modulating a signal generated by the triangular wavegeneration unit 209 shown in FIG. 44, and a condition in which thetransmission signal is reflected from the target and is entered as areception signal. The example in FIGS. 46A and 46B shows an instance inwhich there is one target.

As FIG. 46A indicates, a reception signal, which is a reflection wavefrom a target, is received, with respect to the transmitted signal, witha lag in the right direction (direction of time lag) in proportion tothe distance from the target. In addition, the reception signalfluctuates in the longitudinal direction (frequency direction) withrespect to the transmission signal in proportion to the relativevelocity with respect to the target. Furthermore, after the frequencymodulation (such as a Fourier transform, DTC, Hadamard transform, andwavelet transformation) of the beat signal obtained in FIG. 46A, thesignal has a peak value in each of the ascending region and thedescending region, as shown in FIG. 46B, when there is one target. Here,the horizontal axis of FIG. 46B represents the frequency, and thevertical axis represents the intensity.

The frequency resolution processing unit 222 performs a frequencyresolution on each of the ascending portion (ascending) and thedescending portion (descending) of the triangular wave from the sampleddata of the beat signal stored in the memory 221. For example, thefrequency resolution processing unit 222 performs a frequency modulationinto a discrete time by, for example, a Fourier transform.

As a result, in the ascending portion and the descending portion, agraph of the signal level for each beat frequency, which wasfrequency-resolved in each of the ascending portion and in thedescending portion, is obtained, as shown in FIG. 46B.

Then, the peak detection unit 223 detects the peak value from a signallevel for each beat frequency shown in FIG. 46B, and detects theexistence of a target. At the same time, the peak detection unit 223outputs the beat frequency (both the ascending portion and thedescending portion) of the peak value as a target frequency.

Next, the distance detection unit 225 computes the distance fromEquation (18) shown below from the target frequency fu of the ascendingportion and a target frequency fd of the descending portion inputtedfrom the peak combination unit 224.(Equation 18)r={C·T/(2·Δf)}·{(fu+fd)/2}  (18)

Further, the velocity detection unit 226 computes the relative velocityfrom Equation (19) show below from the target frequency fu of theascending portion and the target frequency fd of the descending portioninputted from the peak combination unit 224.(Equation 19)v={C/(2·f0)}·{(fu−fd)/2}  (19)

In the above equations for computing the distance r and the relativevelocity v,

-   -   C: optical velocity    -   Δf: width of the frequency modulation of the triangular wave    -   f0: central frequency of the triangular wave    -   T: modulation time (ascending portion/descending portion)    -   fu: target frequency in the ascending portion    -   fd: target frequency in the descending portion

Next, the reception antenna 211˜21 n according to the eighth embodimentis an array-type antenna which is placed at an interval d, as shown inFIG. 47.

An incoming wave from a target (incident wave, which is a reflectionwave from the target with respect to the transmission wave transmittedby the transmission antenna 203) enters the reception antenna 211˜21 nfrom a direction at an angle of θ degrees from the axis perpendicular tothe surface of the antenna which is lined up.

At this time, the incoming wave is received by the reception antenna211˜21 n at the same angle.

A phase difference “d_(n-1)·sin θ,” which is obtained by this same anglesuch as the angle θ and the interval d between each antenna, occursbetween each adjacent antenna.

This phase difference can be used to perform a digital beam forming(DBF), which is an additional Fourier transform, in the antennadirection, of the value which underwent a frequency resolutionprocessing for each antenna in the temporal direction. The phasedifference can also be used to detect the angle θ in a signal processingof a super resolution algorithm and the like.

<Signal Processing of a Reception Wave by the Signal Processing Unit220>

Next, the memory 221 stores a time-series data (the ascending portionand the descending portion), which was obtained by A/D modulating thereception signal by the ADC 207 with respect to the wave form storingregion, so that each time-series data corresponds to each antenna 211˜21n. For example, when 256 pieces are sampled in each of the ascendingportion and the descending portion, 2×256(pieces)×(number of antennas)numbers of data are stored in the wave form storing region.

The frequency resolution processing unit 222 outputs a frequency pointindicating a beat frequency, and also outputs a complex number data ofthe beat frequency. The frequency point is obtained by performing aFourier transform, for example, and modulating each beat signalcorresponding to each of Ch1˜Chn (each antenna 211˜21 n) into afrequency at a predetermined resolution performance. For example, wheneach of the ascending portion and the descending portion for eachantenna has 256 pieces of sampled data, the beat signal is modulatedinto a beat frequency as a frequency region data of the complex numberfor each antenna. Thus, the beat signal becomes 128 pieces of complexnumber data (2×128 pieces×data for the number of antennas) for each ofthe ascending portion and the descending portion. In addition, the beatfrequency is indicated by the frequency point.

Here, the only difference between each of the complex number data foreach antenna is the phase difference which depends on the angle θ. Theabsolute value (such as the reception intensity or the amplitude) ofeach complex number data on the complex plane is equal.

Next, the frequency dissolution processing unit 222 performs a frequencyresolution on the inputted beat signal (temporal axis Fouriertransform), and outputs a frequency point indicating the beat frequencyand the complex number data to the DBF processing unit 233.

Next, the DBF processing unit 233 performs a Fourier transform on theinputted complex number data corresponding to each antenna in thedirection in which the antenna is aligned. In other words, the DBFprocessing unit 233 performs a spatial axis Fourier transform.

Then, the DBF processing unit 233 computes the spatial complex numberdata for each angular channel corresponding to the angular resolution,which, said differently, depends on the angle, and outputs to the peakdetection unit 223 for each beat frequency.

Therefore, the spectrum, indicated by the spatial complex number data(with a unit of beat frequency) for each angular channel outputted fromthe DBF processing unit 233, depends on the estimation of the arrivaldirection of the reception wave by the beam scanning resolution.

In addition, since a Fourier transform is conducted in the direction inwhich the antenna is aligned, the same effect can be obtained as whenthe complex number data is added between the angular channels.Furthermore, the S/N ratio of the complex number data for each angularchannel is improved. Thus, the accuracy with which the peak value isdetected can be enhanced.

The above described complex number data and the spatial complex numberdata are computed in both the ascending region and the descending regionof the triangular wave.

The peak combination unit 124 combines the beat frequency and its peakvalue, entered by the peak detection unit 123 and shown in FIG. 29, witha beat frequency of each ascending region and the descending region andits peak value, in a matrix fashion in a round-robin matter. In otherwords, the peak combination unit 124 combines all of the beatfrequencies in each of the ascending region and the descendingdirection. Thus, the peak combination unit 123 outputs, in series, tothe distance detection unit 125 and the velocity detection unit 126, andconfirms the combination at the pair confirmation unit 127. Here, thehorizontal axis of FIG. 29 indicates the frequency point of the beatfrequency, while the vertical axis indicates the level (intensity) ofthe signal.

Next, the peak detection unit 223 detects the peak value based on thespectrum intensity indicated by the spatial complex number data for eachangular channel which is inputted. The peak detection unit 223 thenoutputs to the peak combination unit 224.

When the above detection result is inputted, the peak combination unit224 combines the beat frequency in the ascending region and thedescending region and its peak value, and outputs to the distancedetection unit 225 and velocity detection unit 226. The combination isthus confirmed by the pair confirmation unit 227.

The distance detection unit 225 computes the distance r to the targetbased on a value obtained by adding the beat frequency of thecombination for each ascending region and the descending region, whichare inputted in series.

Further, the velocity detection unit 226 computes the relative velocityv with respect to the target by the difference in the beat frequency ofthe combination for each ascending region and the descending region,which are inputted in series.

In addition, the correlation matrix computation unit 228 selects thebeat frequency, which underwent a frequency resolution by the frequencyresolution processing unit 222, according to the frequency point of thebeat frequency of the pair whose combination was confirmed. Thus, thecorrelation matrix computation unit 228 generates a correlation matrixcorresponding to the beat frequency of either one of the ascendingportion and the descending portion (in the fifth embodiment, thedescending portion) regarding this combination.

Next, the range detection unit 236 outputs an angular range informationto the direction detection unit 230 as information on a direction whichhas a rough (low) level of resolution compared to the MUSIC Method andthe like, based on the angular channel corresponding to the spatialcomplex number data of the frequency point which is the same as theoutput to the correlation matrix computation unit 228 concerning thepair confirmed by the pair confirmation unit 227. For example, the rangedetection unit 236 compares the peak value of each angular channel witha predetermined threshold value. Thus, the range detection unit 236detects an angular channel having a peak value greater than or equal tothis threshold value. When the detected angular channel exists beingadjacent to one another for a number greater than or equal to thepredetermined plurality of channel numbers (for example, four angularchannels), the range detection unit 236 outputs this range to thedirection detection unit 230 as angular range information.

By using the angular range information described above, the directiondetection unit 230 can narrow the detected range of the direction to anarrow angular range by using the spatial complex number data for eachangular channel while performing a computation of the MUSIC spectrum, asshown in FIG. 49A and FIG. 50A, compared to case in which there is noinformation regarding the angular channel. In this way, the resolutionof the calculation of the MUSIC spectrum can be enhanced.

Here, FIG. 49A and FIG. 50A shows an instance in which a Fouriertransform of 16 bites was conducted in the direction of the channel (inthe direction of the antenna) so that the angular dependency Ch(channel) after the DBF becomes 15Ch. Here, when the value of thespectrum intensity exceeds the DBF level threshold value in the range of4Ch consecutive Ch (angles), as described above, the range detectionunit 236 makes a setting of the above described angular rangeinformation, i.e., a narrowed range. The range detection unit 236 thusoutputs this angular range information to the direction detection unit230.

As a result, the direction detection unit 230 performs an analysis ofthe narrowed detection range of the direction with a high level ofaccuracy based on the angular range information inputted by the rangedetection unit 236.

Further, in FIG. 50A, there are two different groups of the spectrumintensity values which exceed the DBF level threshold value in 4Chconsecutive angular range. The range detection unit 236 outputs eachrange (the angular ranges of Ch3˜Ch6 and Ch10˜Ch13) to the directiondetection unit 230 as a first angular range information (the angularrange in FIG. 50B) and a second angular range information (the angularrange in FIG. 50C).

In addition, the direction detection unit 230 detects the MUSIC spectrumin series, with each range of the first and second angular rangeinformation separately (independently) regarded as the angular range forcomputing the MUSIC spectrum. Therefore, it is possible to analyze thedetection range of the direction, narrowed by the angular rangeinformation inputted from the range detection unit 236, with a highlevel of accuracy.

In FIGS. 49A, 49B, and FIGS. 50A, 50B, and 50C, the horizontal axisshows the Ch number of the angular channel, while the vertical axisshows the spectrum intensity for each Ch which was computed during theDBF process.

<Super-Resolution Algorithm in the Estimation of the Arrival Directionof an Incoming Wave>

Next, a super-resolution algorithm estimating the arrival direction ofan incoming wave according to the correlation matrix computation unit228, the eigen value computation unit 231, the determination unit 232,and the direction detection unit 230, is described with MUSIC as anexample with reference to FIG. 51. FIG. 51 is a flowchart describing theflow of the operating process of a general MUSIC Method. Since theprocess of the MUSIC Method itself is used in general (for example, inNon-Patent Documents 1 and 2, or, Patent Documents 3, 4, 8, and 9), onlythe aspects of the MUSIC Method which are necessary in the eighthembodiment are described.

The frequency resolution processing unit 222 reads in the beat signal ofthe reception wave stored in the memory 221 (step S2101), and performs afrequency-modulation on the beat signal for each antenna (step S2102).

Further, as described above, the correlation matrix computation unit 228reads in the complex number frequency region data (hereinafter referredto as complex number data) by making a selection from the frequencyresolution processing unit 222. The complex number data has undergone afrequency resolution, and corresponds to the frequency point of thetarget in the descending region for which a pair has been confirmed bythe pair confirmation unit 227. In addition, regarding the descendingregion, the correlation matrix computation unit 228 generates acorrelation matrix indicating the correlation for each antenna (stepS2103).

The generation of the correlation matrix by the correlation matrixcomputation unit 228 in step S2103 is conducted, for example, accordingto the methods shown in FIGS. 52A and 52B. The methods shown in FIGS.52A and 52B are briefly described below.

According to the method shown in FIG. 52A, the correlation matrixcomputation unit 228 generates a correlation matrix (complex correlationmatrix) based on the bare complex number data (step S2103_1), andprocesses with a forward-only spatial average (Forward Spatial AveragingMethod) or a forward-and-backward spatial average (Forward-BackwardSpatial Averaging Method) (step S2103_2).

Spatial averaging refers to a process in which the number of antennas inthe array of the original reception antennas is divided into subarrayswhich has a lesser amount of antennas, and the subarrays are averaged.The phase relation of waves having a correlation differs according tothe position at which the wave was received. Thus, according to thisbasic principle of spatial averaging, the correlation matrix is obtainedby moving the reception point in an appropriate manner. In this way, thebasic principle of spatial averaging is such that the correlation of thecorrelated interference wave is restrained due to the effect of theaveraging process. In general, the averaging is conducted by taking outa plurality of subarrays having the same alignment from the overallarray of reception antennas without moving the array of receptionantennas, and then obtaining the average of each correlation matrix.

For example, as shown in FIG. 53, when the array of reception antennas211˜211 n is such that there are nine antennas (n=9), the correlationmatrix computation unit 228 obtains the backward correlation matrixCR^(b) _(f) in the latter equation (6) with respect to the correlationmatrix CR^(f) _(f) in the forward equation (5) indicated below. Thus,the correlation matrix computation unit 228 carries out an averagingprocedure of the forward/backward elements by averaging thecorresponding elements in the correlation matrix in equation (5) and thebackward correlation matrix in equation (6) according to the followingequation (20).(Equation 20)CR ^(fb) _(f)=(CR ^(f) _(f) +CR ^(b) _(f))/2  (20)

In this way, the correlation matrix computation unit 228 divides thecorrelation matrix CR^(fb) _(f), obtained by the forward/backwardaveraging process, into subarrays, and computes an average. Thus, thecorrelation matrix computation unit 228 obtains a correlation matrix Rxxwhich is used to estimate the arrival direction of the reception wave.In other words, the correlation matrix obtained by the forward/backwardspatial averaging process can be expressed as follows by Equation (21).(Equation 21)Rxx=(CR ^(fb1) _(f) +cR ^(fb2) _(f) +cR ^(fb3) f)/3  (21)

Here, the correlation matrix computation unit 228 obtains thecorrelation matrix Rxx by dividing the nine reception antennas 211˜219into three subarrays each of which including seven antennas 211˜217,212˜218, and 213˜219, and by averaging the corresponding elements ofeach matrix in the subarray.

Meanwhile, in the case of the forward spatial averaging, the matricesfrom V₁₁ to V₉₉ can be kept as the matrices from W₁₁ to W₉₉ in equation(5). Thus, it is not necessary to average each element as shown, forexample, in equation (22).(Equation 22)V ₁₁=(W ₁₁ +W ₉₉)/2  (22)

Regarding the use in which the arrival direction of the reception waveregarding the radar is estimated, all of the incoming reception wavesare reflection waves caused by the transmitted transmission wavereflecting from the target. Therefore, the data of the reception wavesreceived by each antenna exhibits a strong correlation with one another.Thus, the results of the eigen value computation in the latter phase arenot obtained accurately. In this way, spatial averaging has an effect ofrestraining the correlation, extracting a self correlation, andaccurately estimating the direction of the incoming wave.

Next, the correlation matrix computation unit 230 performs a unitaryconversion in order to convert the correlation matrix of complex data,which underwent a spatial averaging process as described above, into acorrelation matrix of real numbers.

Here, by converting into a correlation matrix of real numbers, the eigenvalue computation in a subsequent step which has the heaviestcomputation load can be executed using real numbers only. In this way,the computation load can be greatly reduced.

Meanwhile, FIG. 52B shows a variation in which the eigen valuecomputation in the subsequent step is executed using complex numberswithout converting into a correlation matrix of real numbers byperforming a unitary conversion as indicated in FIG. 52A.

Further, in step S2103, regarding the correlation matrix Rxx obtained bythe step S2103_3 in FIG. 52A and the step S2103_2 in FIG. 52B, thevalues of each element can be normalized (i.e., divided by the maximumvalue) based on the maximum value of the correlation matrix (or thediagonal element of the correlation matrix).

Next, the eigen value computation unit 231 computes the eigen value ofthe correlation matrix Rxx obtained in step S2103 and its correspondingeigen vector as an eigen value λ and an eigen vector e which satisfiesthe following characteristic equation, outputs to the directiondetection unit 230, and outputs the eigen value λ to the determinationunit 232 (step S2104).(Equation 23)Rxxe=λe  (23)

Then, based on the eigen value λ obtained above by the eigen valuecomputation unit 231, the determination unit 232 estimates the number ofincoming waves necessary to remove the signal component vector (stepS2105).

Here, the determination unit 232 performs the above estimation of theincoming wave according to the incoming wave estimation process,described later.

Next, the direction detection unit 230 generates a spectrum of angles bycomputing an inner product of a vector with only the noise componentsafter removing the signal vector, and a vector for each direction andangle which is predetermined internally (step S2106). As a result, it ispossible to associate a null with a directional characteristic to thearrival direction of the incoming wave.

At this time, the direction detection unit 230 performs a computation ofthe inner product of a vector having only a noise component and adirection vector for each directional angle which is internallypredetermined, only in the angular range indicated by the angular rangeinformation inputted from the range detection unit 236, as alreadydescribed above. In this way, the direction detection unit 230 creates aspectrum P_(MU)(θ).(Equation 24)P _(MU)(θ)=a ^(H)(θ)a(θ)/{a ^(H)(θ)E _(N) E _(N) ^(H) a(θ)}  (24)

Here, a(θ) is a directional vector, E_(N) is a noise sub-space eigenvector, and H represents a conjugate transpose.

Further, the direction detection unit 230 detects a peak from thespectrum of angles which exceeds a predetermined threshold value. Inthis way, the direction detection unit 230 detects the peak and computesthe direction of the incoming wave (angle θ) (step S2107).

In addition, the direction detection unit 230 can make a conversion to aposition in the lateral direction with respect to the vertical axis ofthe array of antennas of the electronic scanning type radar device basedon the angle (i.e., the arrival direction of the reception wave) and thedistance computed by the distance detection unit 225.

A standard MUSIC Method has been described above. In the MUSIC spectrumcomputation in step S2106, it is possible to use a method called theRoot-MUSIC Method which computes a solution from the root of thepolynomial, instead of a type searching with a direction vector.

Here, Root-MUSIC is a method which directly obtains θ that satisfies thefollowing equation (25), and can be carried out without creating aspectrum.(Equation 25)a ^(H)(θ)E _(N) E _(N) ^(H) a(θ)=0  (25)

In addition, after the step S2107 in FIG. 51, it is possible to add aprocess computing the received electronic power and deleting anunnecessary wave (data of an unnecessary reception wave).

In other words, the determination unit 232 compares the electronic powerindicated in the diagonal component of the matrix S in the followingequation with a predetermined threshold value, and detects whether ornot the electronic power exceeds the threshold value. Further, thedetermination unit 232 has a process which makes a determination ofnecessary reception wave when the electronic power exceeds the thresholdvalue, and, meanwhile, makes a determination of unnecessary receptionwave when the electronic power is less than or equal to the thresholdvalue.(Equation 26)S=(A ^(H) A)⁻¹ A ^(H)(Rxx−σ ² I)A(A ^(H) A)⁻¹  (26)

Here, S indicates the correlation matrix of the signal of the receptionwave, A indicates the directional matrix, A^(H) indicates the conjugatetranspose matrix of A, I indicates the unit matrix, Rxx indicates thecorrelation matrix computed by the correlation matrix computation unit228, and σ² indicates the dispersion of the noise vector.

By adding the process, described above, of computing the receivedelectronic power and deleting an unnecessary wave, it is possible todelete the unnecessary incoming reception wave, when the number ofreception waves was overestimated in the estimation of the number ofreception waves in step S2105. Therefore, it is possible to retain amargin of the setting of the threshold value λth and the threshold valueλth′ in the estimation process of the number of incoming waves describedbelow (in other words, even if each threshold value is not set rigidly,the reception wave that does not have an adequate reception electricpower is deleted).

As described above, the eighth embodiment is configured so that thedirection is first estimated using DBF (Digital Beam Forming) which hasa resolution lower than super-resolution algorithms such as the MUSICMethod, thus narrowing the angular range in which the target exists, anda super-resolution algorithm is used to estimate the direction in thisangular range based on the correlation matrix.

<Incoming Wave Estimation Process>

Next, an incoming wave estimation process in step S2105 of FIG. 51 isdescribed with reference to FIG. 54. This incoming wave estimationprocess is used in the detection of the MUSIC spectrum by the directiondetection unit 230. The process of estimating the number of incomingwaves, shown in the flowchart in this FIG. 54, is a process in whichprimarily the determination unit 232 in FIG. 44 uses the eigen valueinputted from the eigen value computation unit 231.

As already described in the flowchart in FIG. 51, at the time when stepS2105 in FIG. 51 begins to be executed, the peak combination unit 224has detected the target, and the eigen value computation unit 231 hasalready computed the eigen value and the eigen vector of the correlationmatrix Rxx.

Therefore, the determination unit 232 assumes that there is at least oneincoming wave, and therefore enters the number 1 into the number ofincoming waves L (step S2401).

Then, the determination unit 232 detects, from among the eigen valuesobtained by the correlation matrix, a maximum eigen value λa which has amaximum value. The determination unit 232 next performs a normalizationof the eigen value λx by dividing all of the eigen values λx (x=1, 2, 3)by the maximum eigen value λa (determining the ratio between the maximumeigen value λa and all of the eigen values λx which includes thismaximum eigen value λa). In this way, the determination unit 232 sets λy(y=1, 2, 3) as the normalized eigen value (step S2402). At this time,the determination unit 232 rearranges the normalized eigen values λyfrom the largest to the smallest.

Next, the determination unit 232 compares in series, the predeterminedthreshold λth and the eigen value λy, in the order from the largest ofthe eigen value λy (step S2403). Then, when the determination unit 232detects that the eigen value λy is greater than or equal to thethreshold value λth, the determination unit 232 proceeds the operationto step S2404.

Then, the determination unit 232 increments the number of incoming wavesL (by adding 1), and returns the operation to step S2403.

Meanwhile, when the determination unit 232 detects that the eigen valueλy is less than the threshold value λth, it is no longer necessary tolater make a comparison between the eigen value λy and the thresholdvalue λth (because the subsequent eigen value λy is smaller than theeigen value λy which is presently being compared). Therefore, thedetermination unit 232 proceeds the operation to step S2405 (stepS2403).

Then, the determination unit 232 confirms the present number of incomingwaves L as the detected number of incoming waves L. The determinationunit 232 next outputs this confirmed number of incoming waves L to thedirection detection unit 230 (step S2405).

In this process estimating the number of incoming waves, thedetermination unit 232 performs the process from step S2401 to S2405described above, every time an eigen value is inputted from the eigenvalue computation unit 231.

In addition, as shown in the flowchart in FIG. 55, before the process ofestimating the number of incoming waves is executed, the determinationunit 232 detects the maximum eigen value λa from the eigen value λxinputted from the eigen value computation unit 231.

Further, the determination unit 232 detects whether or not this detectedmaximum eigen value λa is greater than or equal to a predeterminedthreshold λmax (step S2400). When the determination unit 232 detectsthat the maximum eigen value λa is greater than or equal to thethreshold value λmax, the determination unit 232 performs step S2401shown in FIG. 51 and the steps subsequent to step S2401 in the processfor determining the number of incoming waves. Meanwhile, when thedetermination unit 232 detects that the maximum eigen value λa is lessthan the threshold value λmax, the determination unit 232 does notexecute the process for estimating the number of incoming waves. Thus,the determination unit 232 does not output the number of incoming wavesL to the direction detection unit 230.

In other words, even in embodiments such that an eigen value is obtainedfrom a correlation matrix of the entire frequency point or within arange of the frequency point, it is possible to cancel (halt) theprocess of estimating the number of incoming waves during the estimationof the number of incoming waves. Thus, even if the level of reception islow due to the influence of multipass on the road surface, it ispossible to avoid making an erroneous estimation of the number ofincoming waves.

Next, another process for estimating a number of an incoming wave isdescribed with reference to the flowchart shown in FIG. 56. This FIG. 56is different from the flowchart shown in FIG. 54 and FIG. 55 in that anormalization is not made after the eigen value is computed. Instead, asdescribed in the description of the correlation matrix computation unit230, a configuration may be made such that the correlation matrixcomputation unit 230 performs a normalization by dividing each elementof the correlation matrix Rxx by the maximum value of the diagonalelement among each element of the correlation matrix Rxx, and then, theeigen value computation unit 231 computes the eigen value and the eigenvector.

In addition, instead of normalizing the correlation matrix Rxx at thecorrelation matrix computation unit 228, the normalization process maybe carried out before the eigen value computation unit 231 computes theeigen value, and then, the eigen value and the eigen vector may becomputed.

As a result, the accuracy of the floating point calculation of the eigenvalue computation increases. In addition, it is possible to reduce thenumber of computations necessary for the conversion of the arithmeticalgorithm (such as the Jacobi Method and the QR Method) of the eigenvalue and the eigen vector. In this way, it is possible to reduce thetime spent on the calculation. Further, it is not necessary to normalizethe eigen value in the process for estimating the number of incomingwaves. In addition, among each element of the correlation matrix Rxx,when the maximum value of all of the elements including the diagonalelement is set to be the standard for the normalization, thenormalization process of the eigen value in step S2402 shown in FIG. 54may be executed before the step S2501 shown in FIG. 56.

In either case, the eigen value λx (x=1, 2, 3, . . . ) computed by thenormalized correlation matrix is inputted into the determination unit232, and the process for determining the number of incoming waves shownin the flowchart in FIG. 56 begins. At this time, the determination unit232 resets the number of incoming waves L to 0.

The determination unit 232 sorts the inputted eigen value λx from thelargest to the smallest. Then, the determination unit 132 makes acomparison between each eigen value λx and the predetermined thresholdvalue λth′ in the order from the largest eigen value λx to the smallest(step S2501).

At this time, when the determination unit 232 detects that the eigenvalue λx is greater than or equal to the predetermined threshold valueλth′, the determination unit 232 proceeds the operation to step S2502.Meanwhile, when the determination unit 232 finds that the eigen value λxis less than the predetermined threshold value λth′, the determinationunit 232 proceeds the operation to step S2503.

Further, when the determination unit 232 finds that the eigen value λxis greater than or equal to the predetermined threshold value λth′, thedetermination unit 232 increments the number of incoming waves L (stepS2502), and returns the operation to step S2501.

Further, when the eigen value λx is less than the predeterminedthreshold value λth′, the determination unit 232 confirms the presentnumber of incoming waves L as the estimated number of incoming waves,and outputs to the direction detection unit 230 (step S2503).

In this process for estimating the number of incoming waves, thedetermination unit 232 executes the above described process from stepS2501 to step S2503 every time an eigen value is inputted from the eigenvalue computation unit 231.

Furthermore, as shown in FIG. 57, it is possible to place a step S2500before the comparison process of step S2501 in the flowchart shown inFIG. 56. In the step S2500, the peak value detected by the peakdetection unit 223 after the frequency resolution is compared with thepredetermined threshold value PEAK-th.

Further, the determination unit 232 detects whether or not the peakvalue inputted from the peak detection unit 223 is greater than or equalto a predetermined threshold PEAK-th (step S2500). When thedetermination unit 232 detects that the peak value is greater than orequal to the threshold value PEAK-th, the determination unit 232performs step S2501 shown in FIG. 53 and the steps subsequent to stepS2501 in the process for determining the number of incoming waves.Meanwhile, when the determination unit 232 detects that the peak valueis less than the threshold value PEAK-th, the determination unit 232does not execute the process for estimating the number of incomingwaves. Thus, the determination unit 232 does not output the number ofincoming waves L to the direction detection unit 230.

In other words, even in embodiments such that an eigen value is obtainedfrom a correlation matrix of the entire frequency point or within aspecific range of the frequency point, it is possible to cancel (halt)the process of estimating the number of incoming waves during theestimation of the number of incoming waves. Thus, even if the level ofreception is low due to the influence of multipass on the road surface,it is possible to avoid making an erroneous estimation of the number ofincoming waves.

Moreover, as shown in FIG. 58, instead of the step S2500 in FIG. 57, itis possible to place a step S2500 in which the maximum value of thediagonal element of the obtained correlation matrix is compared with apredetermined threshold value.

FIGS. 59A, 59B, 59C, and FIGS. 60A and 60B are graphs showing acondition in which the distribution of the eigen values actuallyfluctuates for each distance (for each beat frequency). FIGS. 59A, 59B,and 59C present the instance in which one wave has arrived (the numberof incoming wave being 1). FIGS. 60A and 60B present the instance inwhich two waves have arrived (the number of incoming waves being 2).

Here, the horizontal axis of FIGS. 59A and 60A indicates the distance,while the vertical axis indicates the eigen value. In addition, thehorizontal axis of FIGS. 59B and 60B indicates the distance, while thevertical axis indicates the value obtained by normalizing the othereigen value λx with the maximum eigen value λa.

FIG. 59A and FIG. 60A indicate that, in an area within a distance ofapproximately 65 m and 80 m from the target, a region exists such thatthe eigen value becomes small due to multipass.

In addition, as shown in FIG. 59B and FIG. 60B, even if the value isnormalized, the fluctuation of the normalized value itself becomeslarge, and an erroneous estimation of the incoming waves may be madewhen the incoming wave estimation is conducted at a region under theinfluence of multipass.

Therefore, according to the processes of step S2400 of FIG. 55, stepS2500 of FIG. 57, and step S2500 of FIG. 58, a configuration isintroduced in which an incoming wave estimation is not made. Thus, theestimation of the number of incoming waves and the detection of thedirection according to this correlation matrix may be cancelled.Therefore, an erroneous detection result of the direction is notcalculated.

FIG. 59C shows the value of the eigen value λx at a distance of 100 (m)in FIG. 60A, in which the number of incoming wave is 1. Thus, FIG. 59Cshows the difference between the values of the eigen value λ1 in thesignal space and the eigen value in another noise space.

Conventionally, the estimation of the incoming wave was conducted bysetting a threshold value Th for each distance by using the eigen valuesof FIG. 59A and FIG. 60A. However, in the eighth embodiment, the eigenvalue is normalized, and a comparison with the threshold value Th ismade, as shown in FIG. 59B and FIG. 60B. Therefore, as alreadydescribed, the threshold value λth (or the threshold value λth′) is setas one value which is uniform for all distances. Thus, a comparison ismade with the eigen value for all distances. Therefore, the estimationof the number of incoming waves is made easily.

In addition, when the estimation of the number of incoming waves cannotbe conducted, the direction detection unit 230 copes with this situationby way of a method estimating the present distance based on the pastdistance, the relative velocity, and the direction.

Ninth Embodiment

Hereinafter, an electronic scanning type radar device according to aninth embodiment of the present invention is described with reference toFIG. 61. FIG. 61 is a block diagram showing an example of aconfiguration of an electronic scanning type radar device according tothe ninth embodiment.

According to this ninth embodiment, similar to the eighth embodiment,the estimation of the direction for the setting of the range is firstperformed using DBF (Digital Beam Forming) which has a low resolutioncompared to super-resolution algorithms such as MUSIC, thus narrowingthe angular range of the target.

The ninth embodiment differs from the eighth embodiment in that an IBDF(inverse DBF, i.e., an inverse spatial axis Fourier transform) isconducted on the DBF-ed value, thus returning to a complex number dataof a temporal axis. Thus, the accuracy with which the direction issubsequently estimated by the super-resolution algorithm is enhanced.The same reference numeral is used for the configuration which issimilar to the eighth embodiment shown in FIG. 45. Hereinafter, theaspects which are different from the eighth embodiment are described.

The ninth embodiment shows a configuration in which a Ch (Channel)deleting unit 234 and an IDBF processing unit 235 are added to theangular range setting unit 250 in the eighth embodiment.

The DBF processing unit 233 performs, similar to the eighth embodiment,a spatial axis Fourier transform, and outputs the spatial complex numberdata to the peak detection unit 223, and outputs to the Ch deleting unit234 as well.

Here, in the ninth embodiment in the direction in which the receptionantennas are aligned, as shown in FIG. 49A and FIG. 50A, the DBFprocessing unit 233 performs a spatial axis Fourier transform based on a16-point resolution, for instance, and, as a result, creates a spectrumwith an angle unit of 15 angular channels, and outputs to the Chdeleting unit 134 and to the range detection unit 236.

Then, similar to the eighth embodiment, from the spectrum with anangular unit of angular channels, the range detection unit 236 outputsto the direction detection unit 230 as an angular range information, arange of the angular channel which has a spectrum intensity greater thanor equal to the threshold value.

In addition, the Ch deleting unit 234 detects whether or not the levelof the spectrum is continuous while being adjacent to the predeterminedangular range, and, whether or not the level of the predetermined DBFthreshold value is exceeded. Furthermore, the Ch deleting unit 234performs a process converting the spectrum of the angular channel whichdoes not exceed the DBF threshold value to “0,” and thus outputs anarrowed spatial complex number data for each beat frequency as shown inFIGS. 49B, 50B, and 50C.

According to the process described above, when, for example, fouradjacent angular channels have a level which continuously exceeds theDBF threshold value, the Ch deleting unit 234 determines that a targetexists, and leaves the spectrum of these angular channels intact, whileconverting the intensity of a spectrum of another angle to “0.”

Further, the IDBF processing unit 235 performs an inverse spatial axisFourier transform on a spatial complex number data such that thespectrum was narrowed, i.e., only the data of the angular channel regionbeing continuous for the predetermined number of angular channels andexceeding the DBF threshold value is left, and the intensity of the restof the region is converted to “0.” Thus, the IDBF processing unit 235restores the spatial complex number data to a complex number data of atemporal axis, and outputs to the correlation matrix computation unit228.

Furthermore, in order to compute a correlation matrix from the inputtedcomplex number data, the correlation matrix computation unit 228 canobtain a correlation matrix with a good orthogonal characteristic suchthat objects on the roadside and the like are removed and the noiseelement is deleted. FIG. 49C shows an example in which a correlationmatrix is created by the above described method with respect to thetarget cluster of the DBF resolution in FIG. 49B (the term “targetcluster” is used because, in actuality, two or more targets may exist),and the target is divided even further by a super-resolution algorithm.

In other words, the present invention involves an algorithm whichestimates the direction of the incoming wave by making an accuratecalculation of the number of incoming waves and the angle. During thedetection of the direction by the DBF, an estimation of the angle is notmade by a peak estimation for example. Instead, a range (target cluster)in which one or more targets exist(s) is merely extracted. Further, theexistence of one or more targets described above is divided into pieces.

In addition, as shown in FIG. 50A, when a reception wave including areflection component from a plurality of target clusters is received,there are a plurality of angular channel ranges, which exceed the DBFlevel at continuous angular channels, in the spatial complex number dataoutputted from the DBF processing unit 233.

Further, the Ch deleting unit 234 selects the spatial complex numberdata corresponding to the frequency point of the target in thedescending region for which a combination is confirmed by the pairconfirmation unit 227. Then, after performing the Ch (channel) deletion,described above, the Ch deleting unit outputs to the 1 DBF processingunit 235.

In addition, the IDBF processing unit 235 performs an inverse spatialFourier transform on the inputted spatial complex number data, andoutputs the obtained temporal axis complex number data to thecorrelation matrix computation unit 228.

As a result, the correlation matrix computation unit 228 calculates thecorrelation matrix from the inputted complex number data, and outputs tothe eigen value computation unit 231.

The subsequent process for estimating the number of incoming waves issimilar to the process described already and shown from FIG. 54 to FIG.57.

According to the process described above, the range of the detectiondirection can be narrowed when the spectrum of the MUSIC is computed inthe direction detection unit 230, in a manner similar to the ninthembodiment. Thus, the resolution can be enhanced.

In other words, according to the configuration described above, thereception wave divided into reflection components for each targetcluster is hypothetically received in the correlation matrix used in theeigen value computation, regarding the eigen value computation unit 231.Therefore, even if the received reception wave includes a reflectioncomponent from a number of targets which is equal to or exceeded by, forexample, the number of reception antennas and the number of subarrays,the eigen value computation can be carried out without any errors. Inaddition, an application can be made to the subsequent estimation of theangular spectrum and the Root-MUSIC which computes a root obtaining theangle.

Furthermore, because a division is made from the entire detectableangular range to a plurality of angular ranges, it is possible toestimate a maximum value of the number of incoming waves (the number oftargets) within the divided, narrow angular range. Therefore, even ifthe number of incoming waves is not estimated, it is possible to set afixed number of incoming waves, and estimate the angular spectrum aswell as the root for obtaining the angle.

Moreover, after the direction of the present target has been detected,the direction detection unit 230 may store the direction of this targetto the memory 221, and read it from the memory 221 as information foreach cycle after the next direction computation cycle. In addition, inthe direction computation cycle, the spectrum may be computed whileincluding the angular range surrounding the target direction of the pastcycle in the above angular range (the angular range information inputtedfrom the range setting unit 236).

Tenth Embodiment

Furthermore, in FIG. 44, after the direction of the present target hasbeen detected, the direction detection unit 30 stores the direction ofthis target to the memory 221.

In addition, the angular range setting unit 250 sets each cycleinformation in and after the next direction computation cycle, reads thedirection of the present target from the memory 221, and consideringthis direction as a center, adds a predetermined range of a numericalvalue to the front and back, sets an angular range with a center at adirection obtained by the result of this previous detection cycle, andoutputs this angular range to the direction detection unit 230 asinformation on the angular range.

At this time, in the previous detection cycle, when each direction of aplurality of targets is stored in the memory 221, the angular rangesetting unit 236 reads the direction of each target from the memory 221,computes the angular range information for each direction, and outputsto the direction detection unit 230.

Heretofore, the eighth, ninth, and tenth embodiments have been describedbased on a configuration used in the FMCW-type radar shown in FIG. 44.However, an application to other antenna configurations of an FMCW-typeis also possible.

In addition, an application is possible to a format other than anFMCW-type such as a multi-frequency CW and a pulse radar. In addition,according to the tenth embodiment, the estimation of the number ofincoming waves and the detection of the direction were conductedconcerning the correlation matrix corresponding to the beat frequency ofeither one of the ascending portion and the descending portion of thetriangular wave. However, it is possible to perform the estimation ofthe number of incoming waves and the detection of the direction in eachof the ascending region and the descending region, and, perform a peakcombination after detecting the direction. Moreover, the tenthembodiment was described based on the MUSIC Method, which is asuper-resolution algorithm, as an example of the direction detectionunit. However, it is possible to apply the Minimum Norm Method and theESPRIT Method and the like, which performs an eigen expansion in asimilar manner, and is a detection algorithm based on the principle thatthe number of incoming waves is estimated in order to detect thedirection of the incoming wave.

Furthermore, a program executing an operation of the signal processingunit 220 shown in FIG. 44, FIG. 45, and FIG. 61 may be recorded in arecording medium which can be read by a computer. The program recordedto this recording medium may then be read by a computer system, and maybe executed to perform a signal processing which performs a detection ofthe direction and includes a process estimating the number of incomingwaves as shown in FIG. 54 to FIG. 57, in which the number of receptionwaves is estimated. Incidentally, the “computer system” here includeshardware such as OS and peripheral devices. In addition, the “computersystem” includes a www-system which possesses an environment to providewebsites (or, an environment for displaying). In addition, a “recordingmedium which can be read by a computer” indicates a transportable mediumsuch as a flexible disc, an optical magnetic disc, a ROM, a CD-ROM, andthe like, as well as a memory device such as a hard disc which isembedded in a computer system. Furthermore, a “recording medium whichcan be read by a computer” also indicates those which retain a programfor a certain period of time such as a network like an internet, aserver when a program is transmitted via a transmission line such as atelephone line, or a volatile memory (RAM) inside a client computersystem.

In addition, the program may be transmitted to another computer systemfrom a computer system which stores this program inside a memory deviceand the like, to another computer system through a transmission mediumor a transmission wave inside a transmission medium. Here, a“transmission medium” transmitting the program includes a medium havingan operation of transmitting information, such as a network(communication network) like the internet, or a communication line(communication wire) such as a telephone line. In addition, the programmay be such that a part of the above described operation is executed.Furthermore, the program may be a so-called difference file (differenceprogram) which executes the above described operation in combinationwith a program already recorded in the computer system.

FIG. 62 is a conceptual diagram showing an electronic scanning typeradar device 302 and a computer 306 mounted on a moving body 301, theelectronic scanning type radar device 302 transmitting a transmissionwave 303, and the electronic scanning type radar device 302 receiving areflection wave 305 caused by the transmission wave 303 reflecting froma target 304. According to FIG. 62, the computer 306 is integrated withthe electronic scanning type radar device 302. However, the computer 306may be placed at a place separate from the electronic scanning typeradar device 302.

INDUSTRIAL APPLICABILITY

According to an aspect of the present invention, the targetconsolidation processing unit relates the same target in the present andin the past to one another. Then, the target consolidation processingunit performs an averaging process of the correlation matrix. Therefore,regardless of the fluctuation of the distance to the target, the eigenvalue computation in the subsequent direction detection process and thespectrum computation (such as MUSIC) can be performed accurately. Thus,compared to the instance in which the computation is performed using thecorrelation matrix of only the present time, it is possible to enhancethe recognition performance of the final distance and direction of thetarget.

The invention claimed is:
 1. An electronic scanning type radar devicemounted on a moving body comprising: a transmission unit transmitting atransmission wave; a reception unit comprising a plurality of antennasreceiving a reflection wave of the transmission wave from a target; abeat signal generation unit generating a beat signal from thetransmission wave and the reflection wave; a frequency resolutionprocessing unit frequency resolving the beat signal into a beatfrequency of a predetermined resolution number and computing a complexnumber data; a target detection unit detecting a peak value from anintensity value of the beat frequency and detecting an existence of thetarget; a correlation matrix computation unit computing a correlationmatrix from each of a complex number data of a detected beat frequencyfor which the target was detected for each of the antennas; a targetconsolidation processing unit linking the target in a present detectioncycle and a past detection cycle based on a distance and a relativevelocity; a correlation matrix filtering unit generating an averagedcorrelation matrix by weighted averaging a correlation matrix of atarget in the present detection cycle and a correlation matrix of arelated target in the past detection cycle; and a direction detectionunit computing an arrival direction of the reflection wave based on theaveraged correlation matrix.
 2. The electronic scanning type radardevice according to claim 1, wherein, when the target consolidationprocessing unit links the target in the present detection cycle and thepast detection cycle, whether the target is related is detectedaccording to whether or not a distance and a relative velocity obtainedby the detected beat frequency of the present detection cycle isrespectively included in a predetermined distance range and a relativevelocity range estimated by a distance and a relative velocity obtainedby the past detection cycle.
 3. The electronic scanning type radardevice according to claim 1 further comprising a memory unit storing adistance, a relative velocity, and a correlation matrix eachcorresponding to one or more past cycles of the related target, whereinthe target consolidation processing unit generates an averagedcorrelation matrix by weighted-averaging a correlation matrix of atarget in the present detection cycle and a target in the past detectioncycle of a plurality of temporal sequences relating to the target in thepresent detection cycle, makes a correspondence between a distance, arelative velocity, and a correlation matrix of the target in the presentdetection cycle and a distance, a relative velocity, and a correlationmatrix of a related past target, and stores into the memory unit.
 4. Theelectronic scanning type radar device according to claim 1 furthercomprising a memory unit correspondingly storing a complex number dataof a detected beat frequency corresponding to the related target for oneor more cycles, wherein when a target of a past detection cycle relatedto a target of a present detection cycle is detected, the correlationmatrix computation unit computes the correlation matrix from the complexumber data of the past detection cycle; and the target consolidationprocessing unit generates an averaged correlation matrixweighted-averaging a correlation matrix of a target in the presentdetection cycle and a past target related to the present target, andcorrespondingly stores a distance, a relative velocity, and a complexnumber data of a detection beat frequency of the related present targetin correspondence with a distance, a relative velocity, and a complexnumber data of the related past detection cycle.
 5. The electronicscanning type radar device according to claim 3 further comprising adigital beam forming unit performing a digital beam forming in adirection of a channel based on the complex number data of each antennaand detecting an existence and a direction of the target, wherein adirection of the target is detected by the digital beam forming from abeat frequency in a present detection cycle, and a correlation between atarget of a present and a past detection cycle is made based on adistance, a relative velocity, and a direction.
 6. The electronicscanning type radar device according to claim 4 further comprising adigital beam forming unit performing a digital beam forming in adirection of a channel based on the complex number data of each antennaand detecting an existence and a direction of the target, wherein adirection of the target is detected by the digital beam forming from abeat frequency in a present detection cycle, and a correlation between atarget of a present and a past detection cycle is made based on adistance, a relative velocity, and a direction.
 7. The electronicscanning type radar device according to claim 5, further comprising achannel deleting unit wherein, when the digital beam forming unitcomputes a spatial complex number data showing an intensity of aspectrum for each angular channel by performing a digital beam formingusing the complex number data, and an intensity of a spectrum of anadjacent angular channel exceeds a predetermined digital beam formingthreshold value in a predetermined range of a number of angularchannels, the channel deleting unit detects that a digital beam formingdetection target exists in the angular channel, and wherein, the channeldeleting unit replaces a spectrum intensity of an angular channel forwhich an existence of the digital beam forming detection target is notdetected to “0,” and outputs as a new spatial complex number data; andan inverse digital beam forming unit generating a restored complexnumber data by performing an inverse digital beam forming on the newspatial complex number data, wherein the correlation matrix computationunit computes a correlation matrix from the restored complex numberdata.
 8. The electronic scanning type radar device according to claim 6,further comprising a channel deleting unit wherein, when the digitalbeam forming unit computes a spatial complex number data showing anintensity of a spectrum for each angular channel by performing a digitalbeam forming using the complex number data, and an intensity of aspectrum of an adjacent angular channel exceeds a predetermined digitalbeam forming threshold value in a predetermined range of a number ofangular channels, the channel deleting unit detects that a digital beamforming detection target exists in the angular channel, and wherein, thechannel deleting unit replaces a spectrum intensity of an angularchannel for which an existence of the digital beam forming detectiontarget is not detected to “0,” and outputs as a new spatial complexnumber data; and an inverse digital beam forming unit generating arestored complex number data by performing an inverse digital beamforming on the new spatial complex number data, wherein the correlationmatrix computation unit computes a correlation matrix from the restoredcomplex number data.
 9. The electronic scanning type radar deviceaccording to claim 7, wherein when the channel deleting unit detects aplurality of digital beam forming detection targets, a spectrum isdivided for each angular channel range corresponding to each digitalbeam forming detection target, thereby generating a spatial complexnumber data for each digital beam forming detection target, the inversedigital beam forming unit generates a restored complex number data foreach digital beam forming detection target by respectively performing aninverse digital beam forming on a spatial complex number data for eachof the digital beam forming detection target, and the correlation matrixcomputation unit computes a correlation matrix for each digital beamforming detection target from a restored complex number data of each ofthe digital beam forming detection targets.
 10. The electronic scanningtype radar device according to claim 8, wherein when the channeldeleting unit detects a plurality of digital beam forming detectiontargets, a spectrum is divided for each angular channel rangecorresponding to each digital beam forming detection target, therebygenerating a spatial complex number data for each digital beam formingdetection target, the inverse digital beam forming unit generates arestored complex number data for each digital beam forming detectiontarget by respectively performing an inverse digital beam forming on aspatial complex number data for each of the digital beam formingdetection target, and the correlation matrix computation unit computes acorrelation matrix for each digital beam forming detection target from arestored complex number data of each of the digital beam formingdetection targets.
 11. The electronic scanning type radar deviceaccording to claim 2, wherein the correlation matrix filtering unitvaries a weighted coefficient, used during a weighted-averaging, withrespect to each of the targets corresponding to the relative velocity.12. The electronic scanning type radar device according to claim 2,wherein, when a change in a position of the target in a lateraldirection obtained from a direction and a distance in a past and apresent exceeds a predetermined range, the correlation matrix filteringunit varies a weighting coefficient, used during a weighted-averaging,with respect to each of the target.
 13. The electronic scanning typeradar device according to claim 2, wherein a number of past cycles usedwhen the target consolidation processing unit computes an average isvaried corresponding to the relative velocity.
 14. A reception wavedirection estimation method by an electronic scanning type radar devicemounted on a moving body comprising: a transmission process transmittinga transmission wave from a transmission unit; a reception process inwhich a reception unit comprising a plurality of antennas receives areflection wave of the transmission wave from a target; a beat signalgeneration process in which a beat signal generation unit generates abeat signal from the transmission wave and the reflection wave; afrequency resolution processing step in which a frequency resolutionprocessing unit frequency resolves the beat signal into a beat frequencyof a predetermined resolution number and computes a complex number data;a target detecting process in which a target detection unit detects apeak value from an intensity value of the beat frequency and detects anexistence of the target; a correlation matrix computing process in whicha correlation matrix computation unit computes a correlation matrix fromeach of a complex number data of a detected beat frequency for which thetarget was detected for each of the antennas; a target consolidationprocessing step in which a target consolidation processing unit linksthe target in a present detection cycle and a past detection cycle basedon a distance and a relative velocity; a correlation matrix filteringprocess in which a correlation matrix filtering unit generates anaveraged correlation matrix by weighted averaging a correlation matrixof a target in the present detection cycle and a correlation matrix of arelated target in the past detection cycle; and a direction detectionprocess in which a direction detection unit computes an arrivaldirection of a reception wave based on the averaged correlation matrix.15. A non-transitory computer readable medium encoded with a receptionwave direction estimation program for an electronic scanning type radardevice mounted on a moving body to make a computer control an operationof a reception wave direction estimation, the program comprising: atransmission process transmitting a transmission wave from atransmission unit; a reception process in which a reception unit makes aplurality of antennas receive a reflection wave of the transmission wavefrom a target; a beat signal generation process in which a beat signalgeneration unit generates a beat signal from the transmission wave andthe reflection wave; a frequency resolution processing step in which afrequency resolution processing unit frequency resolves the beat signalinto a beat frequency of a predetermined resolution number and computesa complex number data; a target detecting process in which a targetdetection unit detects a peak value from an intensity value of the beatfrequency and detects an existence of the target; a correlation matrixcomputing process in which a correlation matrix computation unitcomputes a correlation matrix from each of a complex number data of adetected beat frequency for which the target was detected for each ofthe antennas; a target consolidation processing step in which a targetconsolidation processing unit links the target in a present detectioncycle and a past detection cycle based on a distance and a relativevalue; a correlation matrix filtering process in which a correlationmatrix filtering unit generates an averaged correlation matrix byweighted averaging a correlation matrix of a target in the presentdetection cycle and a correlation matrix of a related target in the pastdetection cycle; and a direction detection process in which a directiondetection unit computes an arrival direction of a reception wave basedon the averaged correlation matrix.